DMing 3e D&D involves a lot of work -- especially if you're making your own setting, adventures, etc.
I've DMed two 3e campaigns in recent years. In both cases, I ran self-made campaigns (although I did adapt a few things from other sources). By the end of the second campaign I realised that I simply did not have the time or energy to continue DMing 3e. I have a real job!
Switching to 'lighter' systems certainly helped for me (C&C and True20 in my case). If I were to DM 3e again, I would almost certainly have to rely primarily on published materials (which would be less satisfying creatively, but c'est la vie).
I'm not surprised that there is a widely reported 'DM shortage' for 3e, at least among gamers with full-time jobs, family obligations, SOs, etc.
For players considering DMing for the first time, I would recommend using products like the 'Dungeon Crawl Classics' modules from Goodman Games, or something like 'The Lost City of Barakus' by Necromancer Games, in order to keep the job manageable.