With radical ideas it's likely that anywhere can become habitable - there have even been ideas to create floating cities in the thick atmosphere of Venus. But places that require esoteric and ever more complex solutions are obviously less desirable than those that don't. And Mars is 100% 'easy mode' in terms of our first colonization outside of Earth.

Yes, the higher atmosphere of Venus is surprisingly habitable. You call Mars 'easy mode', but you can fill (acid-proof) balloons with Earth atmosphere, and they will float in Venus at more or less exactly the spot that has a nice temperature and pressure for humans to enjoy.