Not a sociologist or a furry but…

If I had to guess it’s probably a combination of various factors: kinks/fetishes being generally more common than we collectively know or talk about, the mass appeal of anthropomorphized characters to the generations of people who grew up with them, the entertainment and general appeal of putting your everyday self aside and portraying a character that you’ve created (see also, vtubers), the furry fandom/community’s general vibe of acceptance and tolerance of just about anyone who decides to identify with it, and so on.

When it comes to the viability of furry art, I think that’s actually much simpler: furries have a ton of pride and identity behind the characters that they create, and so they really value the idea of bespoke artwork that shows off their fursona in the best/coolest/cutest possible light.

Not a sociologist but it’s quite clear that the internet contributes to the rise in popularity in recent years. I feel like childhood exposure to media also contributes to the interest. Anthropomorphic animal characters are everywhere from movies to series to video games.

In addition to all that, the fandom has a very inclusive and accepting culture, so it’s easy to get a sense of community within, which will make people more likely to stay.

I dunno, maybe ask the entire Egyptian pantheon. Or big chunks of the Hindu pantheon.

Or the 35000+ year old sona known as “the lion man”. https://en.m.wikipedia.org/wiki/Lion-man

Or the Leopard Man society from the Congo.

Or the Velites from Rome.

This ain’t new; adopting animal traits and appearance to symbolize aspects of personality is OOOOLD behavior.

Animals are cute, and people like cute things.

Similar to anime, I guess.

Rembrandt had to do porn to make ends meet, it’s not that uncommon.