Future maintenance now has to involve removing the panels, then installing them again afterward. That's a lot of extra work (so, money). Lots of roofers hate solar and won't touch it (they've worked on many roofs solar installers fucked up—talk to some). So now you need two companies involved. You'll have to take great care with the whole arrangement if you want the usual warranty you get with roof work from any decent roofing company (again, many hate solar and will be reluctant to guarantee work that has solar touching it, especially if another company has to do that part, which is often the case). The coordination effort means roofing projects are longer now.

It's just not worth it once you factor in the period to recoup investment on the panels. The extra headache and risk plus long period before you're in the black anyway, just nowhere near being worth it. And all that assumes nothing goes wrong with the panels