Because "all you have to do is put some speakers in and everybody can hear"---------
When do architects get their sleep? During the acoustics classes.
I had a chance to sit down with a couple of architects and ask for an explanation to this very question. Unlike paint, cloth, flooring and wood, you can't "see" the result and it makes it a tough sell.
They do take acoustics in school but trying to sell to the client is nearly impossible.
Hopefully, with these 3D virtual tour video systems, there will be an opportunity to let clients hear the differences in acoustic signatures with different room surfaces.
There has to be an economic incentive to spend the extra $$ on treatment. As long as the public keep coming to shit sounding venues and spending money, no one cares.
In the meantime, we in the audio world, apparently can "fix it" with some kind of voodoo magic DSP