If the pet is a 'premium' pet (crown pet) and you do not already have that body type in your pet tome then you will be charged crowns to hatch for the CHANCE at getting the premium body type.
It's caused quite some controversy as many crown pets are very very common and many crown pets can not be added to the kiosk at all (yet). Hopefully KI will reassess the pricing for old crown pets that are easily available nowadays but until then if you don't have the body type in your tome you will have to either pay crowns, find someone to hatch with you in the traditional way via the sigils or choose a different pet in the kiosk that does not carry the premium charge.
I hope this helps and you get the pet/s you would like
Initially there were basically no crown pets in kiosk. I think the crowns cost was a late addition out of test realm, and then they added extra crown pets at last minute. Probably see more added over time I'm guessing.