It's a bit of both, but it's much more so that they built a lot of them, and then threats of lawsuits basically tanked general aviation production in about 1985 and it's never really recovered - so there is a heavy bias towards older design.

Even the 172 itself was out of production for over a decade (1986-1996). Peak production on the 172 (in the 60s) was ~1400/yr. In 2019 they built 52.