Its straight up gambling...
That seems like a really obvious statement, and to most it probably is. Honestly i kinda knew myself while i was opening the packs that i was just gambeling away all my dec, hoping for that elusive goldem legendary (and i was spoiled by an early goldem summoner) but it was fun and i kept going.
I would take my openings and sell them on to fund more pack openings, and i would often get lucky, soooo many legendaries and so many golds. Yet the prices of the cards fell the more i opened, and my funds to buy more packs slowly fell with them.
So now i am buying up packs to hold and sell on later as i originally planned to do, hoping to recoup the hundreds of dollars lost on what was essentially a very expensive gatcha game.
I had fun, but it stopped being fun, and as the saying goes "when the fun stops...STOP!"