I believe the motivation for CL to make you sign up for an account was to prevent fraud. Rather than listing anonymously, you have to have an account. My understanding is that this is only for categories where stolen goods (bikes) were common, or where scams are common, and where spamming was common.
Fees didn't have anything to do with it. My understanding is that they instituted fees in NYC for housing because the spammers were overwhelming the category, and that if other locations have the same problem, then they too will start charging a minimal fee. Employment is the only thing they had been charging for, and that was $75 a pop. I think NYC housing is like maybe $10 a pop, again, as a deterrent.
I didn't research any of this, but it should be easy enough to google the answer. It's not like CL is trying to be secretive or anything.