they are openings, and many lower players dont understand them, as well as e4 e5.
Why do high rated player's do these move's
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Sorry I can't use a game as an example but I've seen top rated player's use these move's in middle game.
They have specific significances in specific positions, but in general:
h6, a6
(1) prevent B, N (or other piece) from going to g5, b5 respectively
(2) push (mainly) B away from g5, b5 - usually to help break a pin
(3) prepare for g5, b5 respectively
(4) sometimes to make room for the king (after castling) to avoid back-rank mate.
[however, sometimes they are a double-edged sword - in specific situations they are bad moves]
Be7
it is usually played to prepare for 0-0, when there is no other better position to develop the bishop. In rare cases, when there is is no pawn on e-file, to protect the king from R or Q checks/threats, or to break a pin.
I think it's usually to prevent a knight or bishop to move to b5 or g5. Be7 can be to prevent a knight on f6 being pinned.
Would need a specific example. From black, h6 is usually only played in dire circumstances if the king is castled there... it means that g5 must be protected. a6 is usually played in openings like the Najdorf or Dragadorf which ultimately prep for b5 and sometimes a bishop on b7. But this is just a general answer. I don't think its a move that a stronger player is attracted to but probrably what the position is demanding at that point in the game.
Why do high rated player's play move's like h6, a6 or Be7 when playing as black.