One of the problems for residential roof-mounted systems is the wind load that large flat panels introduce. This load needs to be offset with very strong roof penetrations. You need to drive large bolts directly into the trusses of the roof which requires a bit of expertise, and has risks if you knick the edge of a piece of structural timber.
Contrast this with the round tubes used by solar thermal that don't introduce large wind loads, and nearly any DIYer can drill holes in their roof to support them.