How are you determining that there is no gelatin? I can tell that there is gelatin in the stock when it cools, at room temp it will be slightly thick (depending on how much water), from the fridge it will be solid enough to rest a pebble on it without sinking (like Jello which is, after all, gelatin).
As another poster noted, if there is too much water, the stock may never "set" even if it has gelatin in it. I opt for making it too strong rather than too weak, so that it is easier to store and can always be diluted. I think you need less water than you might think. I usually barely cover the bones and use a pot that fits the bones rather snugly, so for say a whole chicken carcass, that wouldn't be more than about 1.5-2.0 quarts of water, less if you chop or smooch the bones together. I keep a lid crooked on the pot so the water doesn't evaporate.
Poultry meat doesn't have much of any collagen in it, it all comes from the bones and the "knuckles" and any connective tissue such as around the breast plate. So I wouldn't worry about cleaning too much meat off of the bones, but you should include the knuckles and all of the hard scraps.
Smaller birds (quails, pullets, etc) tend to have a higher "bone to meat" ratio and are often better for stock. The same is true if you can buy a collection of wings, necks, feet, heads, etc.
If you roast the birds and overcook them a lot, you might be melting a bunch of the collagen out of the bird before you make the stock.
I am not sure what temp most crock pots run at (I never use one), but when I make stock it is slowly simmering, so it is probably around 200-212F. If your crock pot has a very low setting at say 130-150F that won't be high enough to break down the collagen. That usually occurs at around 165F (which is why large bone-in roasts seem to "stick" at 165F during a slow roast).
That is about all I can think of. The most plausible explanation seems to be that you have too much water or too low a temp.