Some players have choosen to invest as much time in the game as the DM in every edition I've played. They didn't need permission from the game to do so.
Now this I find interesting. Outside of chargen, what could a player really do to invest his time in a DM's campaign in earlier editions? Any plans or ideas he may have would have to be vetted by the DM and could be vetoed pretty quickly by in game events. The player couldn't spend time thinking about equipment (completely the purview of the DM), hirelings or henchmen (again, DM), proficiencies weren't exactly time demanding, spells (DM, again). So, what could a player do with his time to add to his character outside of game time?
As far as the Complete Idiot's Guide goes, well, it is true that you can make creating a character very complicated. If the DM allows all books for example, chargen can be a right pain in the petoot. I also think that there are a number of gamers who start campaigns at higher levels, which can exponentially increase complexity.
It doesn't have to, but it can.
To bring up another topic for a moment: I find these conversations interesting in that they outline some assumptions that I never really considered. Take the idea that 1e is humanocentric. This honestly never occured to me. The groups that I played in played mostly demi-humans. I was odd man out for playing humans usually. Later groups added humanoid races like minotaurs and half-ogres. Even the adventures we played rarely featured more than a handful of humans. Slave Lords, while it does have humans, features a lot of humanoids, Against the Giants (duh), Hidden Shrine of Tomoachan, even the low level adventures like Cult of the Reptile God have mostly critter opponents.
Honestly, for me, the idea that no one wants to play humans has always been true in D&D. At best, my groups were about half humans, and usually a lot less. In my current campaigns, the ratio has remained pretty constant.