It’s interesting, some of the lesser sports e.g. “dressage” are incredibly difficult tickets, in addition to obvious things like gymnastics and swim. Every sport has their own group of hardcore fans much like wrestling. There is also a group of people that seems to attend “every” Olympics. For Paris it looks like the “Concorde Urban Project” has become a hot ticket. This is where they do skateboarding, BMX, and I think breakdancing. Probably the novelty.
The IOC has seemed to be doing a good job controlling scalping and reselling, with the only tickets available so far being through them at face value. Tickets weren’t cheap, but were fair.