glad you changed tires, not worth it on a commuting bike to have to deal with a tire issue. You definitely got your monies worth out of that tire.
I guess if you kept an eye on pressures then thats not it, but only you know if you rode them under inflated. If not, then they've just lived a good long life and have cried Uncle.
I weigh over 220lbs and it is only a 20" wheel - undoublty on some days I road it with under inflated tires. Any advice on the best tire pressure to use? Since I live in NYC - I need it to be a 20" folding bike for a few reasons - but I would love a full size bike. 😁