This is a more modern phenomenon with the eBay generation. Back in the day if you had a ticket for a big event you guarded it with your life, but there are many today who don’t see a problem with buying/selling to make a living, some just to get by in life, others who are just greedy.
Looking at the pictures on TV though, Club Wembley and the seats around the “dugouts” look awful these days too, empty seats everywhere. This should have been packed to the rafters for a first Manchester derby final but the lowest non-covid attendance at Wembley since it re-opened is just odd.