Hello, I hope you are all good.
I was wondering why white played b3 and a4 while black can easily defend with b5 and Bb7 in this position.
Well, its not like bb7 is a remotely good spot for the bishop unless white exchanges pawns, is it? White doesn't get much if any advantage out of b3, but its not like the other candidate moves (nf1, a4, c3) lead to anything much either. White has significantly better development but cant really exploit it, and there is a lack of other pawn breaks. Piece play with nf1 is a possible try, but with the white bishop bocked from d3, the options are limited. Its a chess game, but hardly an exciting try.