The ‘Pedestrian’ Who Became One of America’s First Black Sports Stars (atlasobscura.com)

Probably most similar to ultra races, some of which are on a short repetitive loop over x time period (24 hour is "common"). Audience is probably closer to dozens of friends/family compared to packed stands of fans/gamblers, though!

Madison Square Garden in particular seemed to attract a bunch of cool and crazy events. They invented "The Madison" track race that's sort of like a relay race on a bike. Instead of passing a baton, when one partner comes around to meet the other, the moving partner grabs the stationary partner and slings them down the track, hoping to transfer as much of their momentum as possible.

They also used to host six-day long bike races that I think were eventually forbidden for being too dangerous, as i think riders would fall asleep and crash.

Running crazes emerged several times in US history only to fade. One of the was in the 1880s too with cross-US races.

The modern running boom started around 1968 with Dr Ken Cooper's book called Aerobics. He coined that term. Aerobic exercises were the best exercises in his studies. And running and swimming were the most intense aerobic exercises.

Lots of things are rare, but not of great interest to collectors. It would make more sense to reverse the question and ask why baseball cards are so collectible.

I expect the card is of interest to some museums and similar institutions that collect historical artefacts. Just not to baseball card collectors.