Why mystical cards are so cheap ?

Still no so cheap as pre-winter snow globes cards.

coz they are not actually mystical o.o

but there's no use from those cards except for getting higher level. or do i not know something?

Because now we know how work this.

19 June (Steam Sales) Steam will reveal summer cards.

I miss the other summer cards. Those made a mint.

Just a tip, they will never go up.

I stocked 2 sets of the 2013 summer sale cards expecting it go to higher in price, after one year the price didn't increase.

What you should do is try to trade mystical cards for more valuable cards