This is probably true, but they should still be researched in case they become useful in other settings, e.g. Mars, or even places on Earth with poor renewable energy potential

A big problem with Mars is that getting fuel there is expensive, they sometimes have large dust storms, and their atmosphere is very thin. Solar power would work fine there 90+% of the time, but outside of fission, there doesn't seem to be any good technology for powering a human habitat over long periods. A rich thorium deposit on Mars could go a long way in creating a self-sustainable habitat. Some thorium reactor designs are notable for their high inherent safety, which is probably a big concern for any human habitat on Mars for morale reasons (think about how much a fatal nuclear disaster on a Martian colony would scare people about space exploration)