I sometimes develop games and applications through Unity, and in the integrated Unity Asset Store there are plenty of people selling templates and frameworks to start on, so I do believe there's a market for it.
On itch.io I've bought a few asset packs with sprites and sounds. I'm guessing there are also game templates, although I have never looked for them.
I've mostly bought stuff when they're part of a Bundle, so I would look into that to increase the perceived "value".