The main site used for buying stolen/jacked accounts is called ogusers. The screenshots in that article are of ogusers, I recognize the layout.
Most of the people who buy and sell accounts do it for profit and fame. Something among teens these days really drives them to want to be internet famous. Having a 1, 2, or 3 character account name garners attention to these people. 1 letter xbox accounts go for 10-20k. 1 letter social media accounts (twitter and IG mostly) go for anywhere from 10k upwards to 75k. A good amount of the 1 letter accounts on these platforms are bought or stolen, very few original creators own the accounts.
The problem is that people aren't content with getting an account by being the creator of the name. They want accounts by any means necessary. Some of these people do this for a living, they've devised their own secret techniques for gaming the system to get account information so they can game password resets and account retrievals. I know for PSN there is a tightly guarded way to pull the email account and name information from any account. For the most sought after accounts, attackers play the customer support reps like a fiddle. Say the right words and they will happily hand over sensitive information.
Even if you buy an account, there's no telling if you get to keep it. Microsoft has been really trying to crack down on this, and has banned hundreds of original accounts over this. I'm not how PSN handles it. IG has been trying to crack down as well. It is a sad state of affairs. Owning an original account isn't about creating it anymore, it's about how much you will spend to buy that name or who you know that can jack the account. Unfortunately, all these platforms are not setup to handle theft, fraud, and selling. If you lose an account, it is next to impossible in most cases to get it back.
In some cases you can get the account back by providing sensitive account info that only the original owner would know. However, the modern process of 'locking down' a stolen account includes flooding it with fake information to push back the original information past the point of being able to be used.