Because it's a free2play game. Long production times are standard for f2p.
My opinion is, that the production times are okay... some bigger items need a few hours and some only 15 minutes... this depends on the item value.
A example for production times... I play Jurassic Park Builder since march 2014, I'm lvl 65 and I still need some dino-upgrades, because the "production times" are really really long (170h and so on.) That's long....
