Yesterday I finally got around to beating TOME2. It was pretty fun but also very frustrating at times.
I can see the draw to making a variant. There are a lot of things I would have liked to change or implement after going through it.
Typically I don't get this idea playing other kinds of roguelikes. Variants to me seem like something made more for the programmer than for an audience.
Some of them turn out pretty decent for the general public to consume. Things like Sil, TOME, or Zangband. Most just don't seem to be worth the time though.
The average length of a band is very long, and requires a big time investment. Many variants have interesting concepts but are not "different" enough to get invested in.
On the upside some variants that are less interesting for players might attract more attention to expand on them. A lot of the popular variants are based on other variants.