The problem with the rotaries is a result of the technology of the time and funding.

They are inefficient because they lose compressed fuel and air as the seals pass over the holes for the spark plugs, which can be largely solved with laser ignition. They are less reliable because of the design of the apex seals, which can be solved by using a roller instead of a blade. Both of those major issues with the rotary could not be solved with the technology of the 60s-00s and the tiny budget available. There are other issues that hold back the design, but those come down to metallurgy and manufacturing processes. Mazda did a great job trying to make the rotary work and it almost killed them.

The other issue that gives then an unreliable reputation is because you can't treat them like a piston engine and people treat them like a piston engine. Hard to fault the knife for breaking when it was used as a pry bar.