The problem is, they tried that. And now people crow about how terrible a decision it was. How it ruined the game. How it made Fighters able to shoot lightning bolts out of their hindquarters or Warlords able to shout hands back on or whatever other nonsense they felt like spewing about 4e. (That last one actually got used by an actual designer--Mearls--in an actual, official podcast about D&D Next. He immediately said he was joking, or rather "I'm being ridiculous," but for God's sake, did he need to repeat tired, naughty word edition-warring on official channels?)
You can't put this genie back in the bottle. There's a too-vocal, and too-influential, minority of players that really do want spellcasters to simply be more powerful than non-spellcasters--or, at the very least, to be more innately, by the rules powerful, because (as they assert) the DM should always be able to fix any and all intra-party imbalance, and if they can't, well, they're just not a good enough DM yet.