What the h6?
It's the 11th (!) most popular move there in the database and not in the top 5 computer lines.
I'm guessing it's just clueless people parroting moves they've seen good players make or read about and without any opening theory. They might think they're stopping Ng5 with it.

===
If black plays 0-0, your DSB (dark-squared bishop) can play Bxh6. His DSB on the other hand (which is likely to go to e7) will block his queen from getting to the queenside.
You can see that his pieces are too cluttered under these pawns, so their chance to get into good squares is small.