[johngossman]

There's already plenty to go around. It's like paintings in the Louvre, the Mona Lisa is overrun because there's a kind of mythology about it, not because nobody paints anymore.

As another poster commented, there are people who still build with traditional materials and methods. The temples are made of wood and have to be renovated. Some are completely rebuilt, symbolic of the transitory nature of the material world. Enryakuji is undergoing renovations and they had to completely cover it with a metal shed while they work on the roof. But it's still open and you can still visit either as a sacred site or to learn about the traditional methods. It is supposed to finished in 2026.

As far as building new temples. Those monasteries had thousands of resident monks. They were significant military powers they were so populated. Even though the overall population of Japan has grown, far fewer people want to live that life. But again, there's no shortage of temples.