While this may be true in the games you might have participated in, my experience was much different. Saying that something is partially true because you never actually got to use that ability doesn't make it true.
I have two Paladins from 1e and both of them are well into the teen levels one of them is almost level 20. He would be if circumstances were different, but people's lives diverge and groups melt away. It's easier to get a group together with the current system than it is to find players for a game that was mothballed in favor of the new and shiny.
The point being that although you may not want to accept it those classes have always had spell casting ability regardless of whether or not any particular player or group ever actually got to cast them, some of us have.
I wasn't talking about my experience. I was talking about the research WotC did before they made 3e, which indicated that most campaigns did not reach higher levels.