Sure but how do I know that the person I'm buying from legitimately owns the account? Won't scam me? Or try to con me out of my existing account? I'm just saying not everyone is as relaxed about that sort of thing.
Markets are regulated by reviews, seller history and so-on, the same as legal markets and it's generally smooth.
The price is about $2-3 so you are not risking much, there are reviews and ratings. Of course there are scam sites, but once you buy several accounts you quickly figure out which ones are scam and which are not.
Re: stolen accounts, you can examine account details, history and activity after purchase, check for emails from social networks and return stolen account to the owner. The posting usually also mentions registration period (new accounts are unlikely to be stolen). But it seems that registering new accounts is cheaper than stealing - old accounts are much more expensive.
I didn't use the account for any illegal activity, there are just sites that use Google Account as a "verification" that you are not a bot, and to issue bans. And I am not interested in jumping through the hoops of searching a locked smartphone with Google Services and filing a visa application to register the account. I strongly dislike proprietary software and locked smartphones.