Right, so now you're asking what I'm smoking, but seriously, hear me out on this.
First off, we all know that Gortat has played starters minutes for the Suns for weeks (almost months). It hasn't mattered that he's been coming off the bench to do it, but the minutes he's put in has been clearly the bulk. Noone can argue with that.
Second, Gortat has been the link between the starting group and the role playing bench. Take for example the latest game against Dallas, forget that the Suns couldn't hit from behind the arc, Gortat had a typical game, 20/15/3 blocks. But the bench was completely ineffective. They had no presence in the middle to allow the shooters from the bench to hit from the outside (it also doesn't help that Duds started). Gortat coming off the bench allows Robin to work some time against the opponents bigs, not for Robin's benefit, but for Gortat so that when he comes in with fresh legs, the other big is slowed down a bit (ok, so it's only a little bit because Robin ain't doin so hot), and if the other team brings in their second stringer, we all know Gortat is a better C than every second stringer out there, right?
I guess the best thing I can say about why Gortat should not start is the same reason why Dudley shouldn't start either. Neither of them are PREMIERE talents. They're GREAT role players who are MUCH better than any 2nd string player out there. But if we use their minutes against 1st stringers, we waste to many of their minutes. Nash and Hill make Carter, Lopez, and Frye better players and they make Dudley and Gortat better players. But Brooks (and Dragic when we had him) can't make the same leap for Carter and Lopez. But when Dudley and Gortat play with Brooks, Warrick, and **whoever else** Gortat and Dudz make a big enough effort to bring the benches effort up. It's a rotation that has worked well in the past to give us a decent shot at winning games by being fresh at the end of the game. Maybe there's more to it than that and maybe someone can expand on it.