If a heel can't cut a good promo without going R-rated, he's not a very good heel. If a wrestling program can't be entertaining without crude humor, blood, etc, then it's not a good wrestling program. TNA can get away with those things because they're a tiny promotion airing on a cable channel catering entirely to red-state young men. They don't really have anything to lose, since they don't have much to start with. As long as TNA keeps their current course though, that's all their major audience will be, and as someone said, they will be fighting for viewers with monster truck rallies, and stuff like that.
As nrb6304 said, going PG is a business decision, and a sound one at that. Do you think Attitude Era style stuff would fly today on USA and SyFy? Do you think major toy companies would want to license kids toys for an R-rated promotion, and mainstream retailers want to carry them? Do you think grown-ups are going to buy enough action figures, fake wrestling belts, t-shirts, etc, to make up for what they'd lose not being able to sell these to kids online, at toy stores, and at the shows? I quick check of the ToysRUs website shows 12 pages of WWE stuff. Apparently, there is no TNA stuff.