TSR put more restrictions and limitations on the power of casters than WotC has. I'm not so sure it's the right solution, it's a solution that apparently couldn't stand the test of time.
I'm afraid it's just a matter of restrictions not being fun, or at least, not the right kind of fun. I found playing a magic-user back in the day an enjoyable challenge. You had the fun of casting just the right spell to really accomplish something cool - once in a while, when your had picked the right spells, and waited to use just the right one at just the right time... you also got a fair amount of frustration, that way.

I'll bet you had similar experiences... I'd speculate that a lot of other once-long-ago players were entirely put off by that process.
Presumably a lot of newer players would have been too ... tho, again, it could just be a matter of what the community has become accustomed to over WotC's tenure.