It's not. When I first got dogs I had them on the ground and I clean it frequently but they still smelled. I then built an above ground kennel which was way cleaner and they didn't smell as bad. I did put some horse stall clean stuff under their kennel during the summer to help keep the poop smell down.
I'm just eliminating all the possibilities here. I know concrete would be even more cleaner but expensive. My dogs kennel is 6' wide 16' long, bigger than most.
Ammo- smart with the above ground kennel, might want to add some 22A stone under the kennel. Its used in driveways and gets hard like concrete yet can be moved around.
The powder barn lime will help with the smell. During the summer maybe remove 2-3 inches of the dirt under the kennel and add the 22A stone. It will get better with you staying on it.
If the dogs smell don't be afraid to give them a bath, I have done that with some that are looking or smelling dirty.
A lot of times they will roll in racoon crap deer crap and they definitely stink. JMO