That up to 4e, it was entirely possible to choose how much you wanted to get involved in combat. Then they decided to silo spells and took away the choice. In 3.5 I played a lot of sorcerers, and out of them only one was a blaster, the rest relied on weapons for combat -if they had any comabt capability at all-. Enter 4e and ALL sorcerers suddenly became blasters, I also played lots of rogues, most of them conmans, charaltans or even just very cunning people, only a few focussed on milking SA damage on the battlefield. Enter 4e, all rogues became skirmishing thiefs, whether you wanted it or not.
The same can be said about clerics and healers, a high focus on out of combat that got taken away on the transition to the new edition. You no longer could preppare only heals and fight the mundane way -or opt not to fight at all-. Also the emphasis on combat delayed the inclusiion of illussion spells,a nd when they got added, BAM they also made damage.
The biggest reason: "Why should I be gimped on the things I want my character to be good at in order to be good at things I don't give a damm about?"