Why Trading Card get less and less?

[Sleeping Forest]

I am a true collector of Trading Card. It includes Basketball (Mostly Michael Jordan) and Superhero (DC and Marvel). But recently getting less and less.
Why? Selling Card can make easy money. Why don't do that? Unreasonable. And Jordan Card get less and hard to buy it? Why? He got so many fans? What happening?

[Sleeping Forest]

see !

[ONEYE]

Maybe you should be not such a true collector?

[Comicbookguy]

Because the ES is way too high and flooded the internet.