Similar marketplaces: https://flippa.com/ https://microacquire.com/
A friend of mine is doing this as his day job through MicroAcquire. He's bought a few businesses so far and is writing a blog about his experience: https://microangel.so/ So far, it looks like he's having fun but putting in a lot of work. He seems to be doing a lot of little code updates and fixes when apis change or other little things break.
Maintaining DNS records and SSL keys is not 3x as hard for 3 domains as for one. Probably neither are taxes. Or keeping on top of security fixes for projects using the same tech stacks.
There’s a couple groups out there who do something like this for public sector projects, sort of taking over the devops aspects and keeping the lights on. And in that case creating project generators could be feasible as well, because it’s easier to run a project that’s built the way you prefer them to be built.