So far, on every rv that I have done an extended warranty inspection on, the tires were 6 or 7 years beyond the DOT code. Just an interesting factoid, which is probably why the general consensus from the threads I have read is that if you buy used you usually can expect to have to replace the tires immediately...assuming you are safety conscious and tend not to push the safety edge and tend to have spent time learning the less obvious things about your rv.
I would speculate than new rv owners who did not own an rv before, often have low maintenance knowledge except for those items of more auto common knowledge, like an oil change. Water heaters are a good example of out of sight, out of mind, commonly neglected items that are not on an auto.
And then you have the if it isn't broke don't fix it, if it isn't flat or you didn't have a blow out, don't change it crowd.