Why isn't there touch move online?

Like if you touch a piece OTB you have to move it, but why doesn't the same principle apply online?

Why aren't there mouseslips OTB?

A very pertinent question indeed.
As picking up a piece with the mouse ... hovering over a square (visualizing the position) then returning the piece to it’s original square and playing another move-

Violates the OTB touch move rule.

It could be said - an unethical practice.
But everybody does it - Why is it permitted? As chess interfaces are written, the practice can not be prevented. But I suppose it could be so programmed - click on a piece and it must be moved. 
The practice is a form of outside help. Allowing pieces to be picked up, any number of them, hovering over a square and deciding on another move.

An outrage ! The practice is not in keeping with the spirit and ethics of OTB play.
It has become so ingrained and accepted as standard practice that it will never change. 
Perhaps a program will be written in the future - click it ... move it !!

Not the point. Keep your mouse off the pieces until a move is decided. Click on it - it must be moved. No such thing as “miss-touches” in OTB allowing another move to be played. Touch it ... move it. If online were to truly mimic OTB - click it ...  move it. Changing to another move would not be permitted. 
The practice is so ingrained players universally think nothing of it, don’t give a second thought to using a visualization tool as outside help.

In OTB play, if the power goes out in the playing hall, do the players who are on the move automatically lose?

Why not? It works that way in online play! You get disconnected, you lose.

OTB?

Other differences:

• OTB you need to hit the clock and lose time doing so.
• You promote by swapping peices and lose time doing so.
• You need to move two pieces to castle and lose time doing so.
• You need to have clothes on...I assume.

I'm OK with on-line having different rules than OTB. 'Cause who wants to get dressed just to play chess. 

You also need to use the same hand to move the pieces and hit the clock.

... even if you're dressed.

The piece must still be physically moved after clicking on it.

This is no accident.

Hover the mouse over the pieces online - same as hovering a hand OTB. Drop down to touch a piece or click on a piece- it’s the same action. Online - pieces are not accidentally moved because they are clicked on (unless only move). They must be physically moved by the mouse. If the touch move rule that applies OTB is followed - then this piece must be moved. 

I’m not advocating for the practice to end - to rewrite chess programs to accommodate the OTB rule. 
Only pointing out that the practice -

is of outside assistance in nature and contrary to OTB rules

The disciplines have quite a few differences of rules. This ability to pick up pieces online - hover over squares and visualize the position (then change your mind and move another piece) will likely be with us forever. 

I think it’s like everything else. Chess programs originally operated in this fashion permitting the practice which became the norm. Players approved of the assisted help. Would be up in arms after years off playing in a certain way. Chess sites are not about to rewrite programs and disgruntle members. 

I wonder - just how many players understand that the practice is of outside assistance for deciding which move to play? 
It is a luxury that online affords - the ability to concretely visualize one move in advance and change your mind - one that OTB does not afford.

And just what is the difference ??

What mistake is made ??

The mouse pointer is hovering over a piece - it requires physical purpose and intent to click on the piece. This is necessary to move the piece. The action is completely intentional- the action does not occur by accident. 
Click it - move it. (online) would be equivalent to
Touch it - move it. (OTB)

But online allows for the opportunity to change ones mind and play another move.

The topic asks why is the practice permitted.

I suggest it is about the original programs as they were written to facilitate online play. We do not know the motives or reasons that allow for the practice but I suspect it is more about ease of programming a workable interface for playing. Online a move is determined, made final by the dropping (release) of the piece. Simple. Programmers afforded players the opportunity to change their minds and not move the piece if it wasn’t dropped. Not only that - players could return the piece and move a different piece! 

Why? How come? It has nothing to do with possible perceived mistakes, ease of use, hardware used or any of that- but rather ease of programming. The original programmers afforded the luxury of allowing a move to be changed if the piece is not physically released once touched. This could have been written differently at the beginnings. The practice became the norm and is not about to be changed. Online players enjoy the luxury of visualization of 1/2 move in advance. One that OTB rules prohibit. Players would shout bloody epitaphs is they could no longer   visualize positions by picking up any piece and seeing just how the position looks and not being able to change their minds.

Ironic isn’t it? The practice is clearly of outside assistance in deciding which move to play. 100% illegal OTB.

Interestingly - it would be in violation of fair play rules  to move pieces about in the same manner on a 2nd physical board being used in conjunction with an online live game (being regarded as analysis). Yet not so to pick up the pieces and move them about on the primary online board. Quite the contradiction.

Chess.com said somewhere that they don't consider it cheating anymore because there's no way to detect it

It's because over the board it's extremely annoying when someone moves the pieces around with no intention of playing them. It disrupts the game. Online your opponent isn't bothered. 

it's not the same thing at all.