From my perspective, the Sun & Moon alt arts first started catching some steam when there were unfounded rumors of alt arts going away in the Scarlet & Violet era. This irrational fear caused some short term spikes in Sun & Moon era alt arts (I made a thread on this topic a while back).
Now many months later, it’s easy to see that the interest in Sun & Moon alt arts is genuine. I believe that alt art collectors want to “catch them all,” which conveniently began to include the long-neglected Sun & Moon era.
When I attend trade nights and speak to vendors in my local community, alt arts are treated as liquid as cash. It is actually crazy how quickly they sell at in person events. It’s just the way of the world right now.