Why do trucks use nitrogen in their tires?

Truck tires filled to 100 psi still have a moderately high PP of O2, and they get retreaded multiple times in an effort to get upwards of 250K miles out of them; under those circumstances, it’s important to minimize aging and embrittlement of that carcass material, so there may be an advantage for these guys.  I say “may” because I haven’t yet seen any positive results publicized by someone other than nitrogen vendors.

Whether that benefit exists or not, there is still the matter of slower pressure loss as described earlier; the economics of a nitrogen inflation system versus the labor involved in regular pressure checks on an 18-wheeler may make sense for them.