Fun scifi hypothesis - the only stars that don't go supernova as a part of collapse into a black hole are ones that are engineered to do so by the locals.

This makes sense.

We'd be seeing a lot more supernovas in the night sky if all/most stars had to go through one.

Only stars significantly bigger than the Sun go through a supernova explosion, and such big stars are a small fraction from the total number of stars.

Moreover, the rate of seeing supernovas depends both on the number of stars that can become supernovas and on the lifetime duration for such stars.

Therefore, even in a hypothetic world where all the stars could become supernovas one might see a very small number of supernovas if the lifetime of stars were great enough.

Thus the frequency of seeing supernovas is not sufficient for any conclusion, without taking in consideration the proportion of stars susceptible to become supernovas and their average lifetime.