In short, prison abolition isn't about abolishing prisons?

Bad name choice in my opinion, as it immediately makes me think: what a dumb idea.

This is kind of like saying being anti-war is a dumb idea because there will surely always be wars fought in defense. Being anti-war isn't necessarily being an absolute pacifist. It's about opposing war and striving towards a future where war is a relic of the past. Everybody understands this, but struggles to apply the same logic to other topics.

Striving for intentionally utopian and impossible ideals is a great idea, actually, as long as you recognize it for what it is. I'm a prison abolitionist. Ultimately what I strive for is a society that doesn't need prisons. I don't know if total prison abolition is possible, but worst case scenario, we get as close as possible. What's so bad about that?

Similarly, I'm a communist, in the classical anarchist sense: abolition of state, class, and money. Are these things possible? Maybe not. In fact, probably not, at least not in any timeframe where humanity will be recognizable to us, as it would require true peace between all people and absolute post-scarcity in every way available to everyone. But worse case scenario, we get as close as possible.

Ultimately, adopting a utopian ideal is a recognition that the struggle to do better never ends. We're never "done". There's no end of history. Even if we do somehow achieve it, it must be maintained.