I was referring to greenfields projects, but the problem is even more acute for the maintenance problem you outline. You have a portfolio of front end projects:

I was referring to greenfields projects, but the problem is even more acute for the maintenance problem you outline. You have a portfolio of front end projects: each one would involve learning whatever quirks the framework and implementation were used (by necessity). A company with a reasonably consistent back-end architecture, project structures and coding practices would have an easier time onboarding maintenance developers, as long as each project was done with some kind of eye to maintainability.