You're being naive, and haven't demonstrated that you know anything about astronomy, or optics in general, really. Astronomers are very cost-conscious, which is exactly why the decadal survey exists - to direct limited funding to projects with the most scientific bang for the buck. All options are considered and the fact that they're being done the way they are is because that is the most effective way to do it, not because people are 'stuck' in the old ways. Astronomy has always been about innovation.