its fairly common for them to have tail loss, most adults in the wild will not have their tails, but it is nice, and shows tremendous husbandry if an adult crested does have its tail
I've had one drop their tail in the middle of the night with no apparent reason to do so. They were not housed with another or even near another crestie and no stress factors. Sometimes they just drop.
It probably seems more common because they don't grow back. they have very sensitive tails so it's hard for one to go it's whole life without ever dropping it.
In the wild, it's almost certain to find one tail less in captivity it's still quite common. You probably see it more in cresties than leos because leos regenerate their tails.