According to recent statements by Ryan Dancey, apparently it's a strategy to have a super bare bones campaign setting out there for DMs who find assembling the maps and gods to not be something they want to do, but want the freedom to fill in most of the rest on their own.
And, it should be noted, it's not that there's NO support -- all the generic supplements tend to have Oerth-based content in them. Not as much as 3.0E had, but it's still present.
But I wouldn't think that, say, one good Greyhawk product a year (even if it just picks the best of the RPGA stuff from the previous year and maybe cleans it up a bit) would mess with their strategy too much.