Yet, they tried. No doubt it's a matter of tastes, but they have done something that no other video games company would have. I'm kind of bored of reading people saying "Blizzard is not what it used to be", as far as I'm concerned I enjoyed D3 and it does not "suck". I have no issue with splitting SC2 in 3 games either, and yet I'm one of the first to complain when games are offering DLCs no longer than a week after their release (SF4 is worth $120 of DLCs... no comment...)!
Of course Blizzard does bad choices once in a while, and one may think they tend to do it a lot lately, but from what I know about the company, it's pretty much all about waiting. Their games are not that good when they come out, it's only after years of feedback that they can start changing it and making it better. In the meantime, fanboys will whine and complain... If you want to see for yourself, just compare the vanilla version of WoW and what it has become now. It's pretty much like night and day! Comparing the vanilla SC to its expansion is like night and day as well, so you should expect SC2 to be what it's supposed to be when the last expansion will be released. Bored of waiting? Then play other games, there are more than enough to fill your needs.