Development
Why Bg4? Why invite the bishop exchange with knight?

Development
I don't think this is a great answer, you could also develop the bishop to d7 or b7 but the engine thinks giving up the bishop pair is better.

Development
I don't think this is a great answer, you could also develop the bishop to d7 or b7 but the engine thinks giving up the bishop pair is better.
Wrong. Bg4 develops the Bishop to a great square and if White spends time with h3 then Black gets the Knight to d5 with an extra tempo. Black has solved most of his problems. Bd7 is placing the Bishop a an important square and blocks the Queen. Bb7 is not even possible right now. The Bishop pair can be nice, but it is not near as important as development, centre, space or King safety.
Why Bg4? White can simply reply with h3. Then Bxf3 Qxf3. Why giving up the light square bishop that easily? I don't get it.