Why trailer tire probs????

I'm pretty sure I see a higher percentage of TT and 5ers pulled over because of tire problems than the general population on the highway. In many cases they are somewhat older trailers, I suspect with old tires. A specific recent example I recall was an older gentleman changing a tire at a rest area. Since I was stopped anyway and he looked like he could use some help, I went and offered my assistance. His trailer was probably 10 years old and I suspect the tires were original. The spare he put on the ground was badly weather cracked. Obviously nothing statistically sound here, just my gut feeling.