I've seen the same question asked about aquarium fish, and parrots too. Macaws, cockatoos, greys - they have human life spans! Just how many of these high maintenance birds can the bird fancying public realistically absorb and care for? 'Toos are beautiful, but it is the rare person who proves they can put up with one long term. Like the giant snakes, they are generally very hard animals to live with.
I've also wondered the same about tortoises. Again, something like a hundred year lifespan. They fascinate me, but even a small Hermman's needs a big (as in 8X4 foot tortoise table, with heat, and UVB. Not a cheap pet! At least the snakes can be stashed in a rack.
I know of only one other person (a local science teacher) who also keeps snakes. In my social circles, they are generally seen an an ...uhmm, unusual pet choice. In general, I think snakes are less likely to be impulse buys than the pretty birds, and the more striking fish, like oscars. The show scene, however, may be different. I've never attended a reptile show.
So back to the original question: where do they end up? I hate to think about it.