Why is Ruy Lopez Steinitz Defense so popular in online games?

I've been looking at some opening statistics and found this opening is almost never played at master level but is played many millions of times online and more often than the Berlin Defense and any other choice besides 3...a6

Batsford chess openings explains why it is rarely played by masters: "The move is sometimes called the Old Steinitz Defence because it is viewed as not best for black. The e5 is not threatened by Bxc6 so there is no need to defend the pawn. Black allows his light square Bishop to become active, but at the same time his dark square bishop is getting blocked, so there isn't much of any gain in development. The move also allows white to play d4 immediately."

However the amateur win rates show that black does almost exactly as well whatever 3rd move is played at the amateur level so can't be considered bad for the average player. Why are so many players attracted to this opening? What is its appeal?

3...d6 is a very popular third move across all time controls including daily chess.

The only explanation I can think of is wanting to protect the pawn structure because if 4.O-O then 4...Bd7 is almost always played.

It is used cos its useful and convienient to be able to continue without having to worry about the E5 pawn

same reason philidor defense is. It is a simple but cramped solution to the complexities of the double king pawn opening

but just because a lot of weak players play it, doesnt mean its bad. GM DZINZI has a two part video series on how to play it here in chess.com. I sometimes play it when i dont want to play the declined nimzowitsch defense.  (1.e4 nc6 2.nf3)

Thanks, I found them and will give them a watch

https://www.chess.com/video/player/ruy-lopez-steinitz-defense---part-1

https://www.chess.com/video/player/ruy-lopez-steinitz-defense---part-2

It is not entirely accurate to say the e5 pawn is not threatened.  In fact, it is threatened, but it is defended tactically as long as White's king is in the center and his e4 pawn is undefended.  Playing the early d6 avoids having to either know the lines or calculate if the pawn is still tactically defended every move.  The main drawback is it leaves Black's dark-squared bishop passive and Black's position a little cramped, but neither of those things are going to be decisive at the lower levels (hell, they are not even decisive at the master levels).

I am not sure what you were trying to show as I pointed that out in the comment you quoted.

Its played online because it wins online. Online chess is not Master chess understand

It doesn't have a particularly good winrate.

Blitz/Rapid/Correspondence: black wins 43% of the time, white wins 52%
Classical: black wins 42% of the time, white wins 53%

At the 2000+ rating levels white wins 57% of the time.

Yes but its easier and more simple to play.. overall winrate doesnt matter if it works for you.. personally I dont like it visually but I dont play E5 I play Sicillian, I just dont like how ehite gets more activity

I run into this a lot when I try to play the 4 knights in online blitz games. I have found it rather challenging to play against, However, quite often when I analyze the game afterwards, the engine finds an easy way to get an advantage. Here is an example.

I think the reason it is played online so much is that it may be easier to try to trade pieces in the stenitz than in the mainline ruy lopez and a lot of online players like to use the strategy of tradiing off as many pieces as possible.....especially in blitz games.

I have also recently encountered it in a OTB G30 game. My opponent was totally blitzing out moves early on, so I felt the need to throw him off. So I took on d4 with my queen. Its probably not the best move but it worked out for me that game.

Can you break the results down by rating ranges?  My instinct is that this variation will be over-represented by sub-1500 players, and even more so by sub-1000 players, and relatively new-to-chess players who are playing theory-free.

Logically, it represents "reasonable" if excessively defensive moves.  d6 makes a lot of sense if you see that the Nc6 will be pinned and the e5 pawn is attacked.

Well, it's playable, and that's really all that matters to a lot of players. You see things like the Philidor, Owen's Defense, Czech/Small Center Pirc, Bowdler Attack Sicilian, Old Steinitz Ruy Lopez, Marshall French, Hillbilly Caro-Kann, et cetera all the time, because they're playable and not worth knowing how to play against, so nobody learns how to beat them.

Knowing how to punish sub-optimal moves requires perfectly optimal play, and that isn't something anybody below 2000 can do, and gambits still take out GMs on occasion, so there's something to be said for them. If something is a system, playable but not the best, people who play chess casually will always be drawn to it as they don't really have any interest in improving long-term, they're just playing to have a bit of fun on a break or an afternoon off or something.