why two knights vs king should not be automatic draw

Chess.com says that since it is not possible to force, it is a draw.

However, you cannot force a win from the starting position.

But the starting position is not considered a draw.

It might be true, but we don't know for certain that a player can't force checkmate from the starting position. More importantly, imagine all that wasted time if players could play moves indefinitely which don't advance the position, with no chance of a win other than their opponent resigning from boredom. The case of insufficient material, like other draw conditions exists to prevent the pointless exercise of waiting for both players to agree to a draw. Add in the fact that online Chess is very often time controlled and I think you can see that minimising cases where the outcome is determined by which player can idle the fastest makes a lot of sense.

if run out of time, it becomes draw by timeout with insufficient material

Laws of Chess:
"5.2.2
The game is drawn when a position has arisen in which neither player can checkmate the opponent’s king with any series of legal moves. The game is said to end in a ‘dead position’. This immediately ends the game, provided that the move producing the position was in accordance with Article 3 and Articles 4.2 – 4.7."
https://handbook.fide.com/chapter/E012018 
A series of legal moves exists that leads to checkmate, hence no draw.

FIDE matches on short time controls without increment sound prone to a lot of flagging.

#5
Without increment is prone to a lot of flagging.
KR vs. KR is a flagging contest under FIDE as wel as USCF and occurs more than KNN vs. K.

bruh..
I believe that if you play king and rook vs king and rook in otb you can just call arbiter and said that its a draw..  trying to only flag your opponent without any other plan is not legitimate strategy to win in classical chess..

The tournaments that I have played in used a five second time delay.  That is more than enough to prevent being flagged.  It's boring and frustrating to make 50 aimless moves, but if that's what my opponent wants to do, so be it.

You can request that the TD declare the game a draw, but they may deny the request.  

I would at least try to request that.. If there is no increment (its not usual but and I have played things like two hours without increment..) then its very legitimate request..   and if there is an increment well then its just pointless playing longer and I don't really know why would anyone do that... I have never seen something like that at otb tournament

I've never had it happen otb, but I would probably make a request.  I've had several KR vs. KR games on Chess.com.  Usually, I have had sufficient time to make 50 moves.  Every so often, I get bored, and hang a piece around move 30 or 40.

#8
"king and rook vs king and rook in otb you can just call arbiter and said that its a draw"
++ The Laws of Chess have no such rule
https://handbook.fide.com/chapter/E012018 

There is such a rule in the link what you sent paragraph III.5.1 games without increment it says:

"If the arbiter agrees that the opponent cannot win by normal means, or that the opponent has been making no effort to win the game by normal means, he shall declare the game drawn. Otherwise he shall postpone his decision or reject the claim."

playing rook vs rook only to flag your opponent is a perfect example of that..