What is the cause? SFMOMA is hideous. MoCA is only better because less of it sticks out of the ground. The LACMA campus looks like shit and makes no sense. Hammer is just a domino box, and if the Norton Simon didn't have the sign it could easily be mistaken for an abandoned Robinsons-May.
Is it a proselytizing thing? Churches and mosques want to bring people in whereas museums want most people to stay out? This would explain the crappy architecture of most synagogues.