Don't know why you said that. Seems a tad illogical to mix PTO applications with a dedicated mower for the sake of an illogical snarky remark.
They make both belt driven rototillers and ones that just need be towed, and a garden tractor gives you a small machine with a transaxle capable of holding up to the stress. Add to that, the availability of the sleeve hitch and compatible implements and you've got a bit more flexibility of use. They're not so common as they were prior to be supplanted by the subcompact tractor, but they're still quite capable machines when used with realistic expectations; or rather they can do a whole lot, just a lot slower.
As for mowing, zero-turns aren't for everyone; I mow at quite a leisurely pace because it's what I enjoy, so the slower top speed of a garden tractor is fine with me. I had a Cub XT3 GSX prior to my Deere and it was, prior to the Deere, the most enjoyable lawn mower I'd ever operated. It was sturdy, comfortable, easy to operate, and had an excellent cut. Now, it had it's issues, but that's more of a brand specific issue lol.
Anyhow, point being that garden tractors have their place, even if it's an ever-shrinking portion of the market.
Now, on the used market they're still extremely popular and at least until recently, reasonably priced.