I am just a home-machanic and in my 7 years of TT’s I have found two broken springs, one broken shoe liner and one blown grease seal. This is why I pull each tire every spring I just want to know what’s going on. If I am going to do a big trip during the year I lift each wheel and spin, like you did. It just makes me feel better to put my hands on them.
So while I don’t know why it happens I do know it can happen, under normal use.
2011 Wildwood T26BHXL
2004 Yukon XL Denali
43yrs of camping; one lucky guy