I disagree that it is primarily about development.
This is a very common theme, and it comes down to the fact that e5 is not easily defended by a pawn (aka "artificially isolated"). Bg4 soon will trade one of the e5-pawn's defenders, and it will need constant watching. It is not a big deal that you will be trading the Bc8 on f3 since white already traded on c6 so you are not giving up the B-pair, and after e6, the c6-d5-e6 complex keeps a nice hold on the light squares.
Black can attack the e5-pawn with Qc7, and Ne7-g6 as one plan. If White defends with the obvious Re1 and Bf4 (and later Bg3 after Ng6), then Rb8; b3 will leave White's dark squares very weak.
It is also important to note that defending e5 with d4 is also never good after cxd4; any c5 and another pc5 appears and a nice center for Black.