People who sell such accounts don't claim these games in their own personal accounts. They create new accounts just to claim the offer and sell those accounts after the bug is over.Unlikely, you are forgetting folks have got years worth of free games collected there. In I was just checking my epic account & to my surprise my game collection on epic has now grown to a massive 11 pages. Each page containing 24 games totaling to a huge collection of ~250 games. Interestingly, I have only played 3-4 games extensively yet & two of these games were then ones that I actually paid for(HZD & CP:2077).
I have seen the same trend after claiming GTA 5 on EPIC. or after UBISoft bug.