One would think the executor would notice the bill in the mail or read the letter that the unit is in arrears and up for auction. Legally, the owner must be notified of such action and given X amount of time to make payment.
Remember for most folks the executor is just one of the relatives, there’s no real estate to worry about. I was co-executor for my grandmother, once you forward somebody’s mail for that you find out just how much complete crap people get in the mail. I still get stupid crap in the mail for her and she’s been dead almost 7 years. And a lot of the bills you just chuck, it’s actually bad to start paying the bills of the deceased because that sets a precedent that you are accepting their debt, so we generally just glanced at stuff to make sure it wasn’t inbound money, we knew about all her property. It would be easy to miss something like a storage locker mixed, just another bill you’re not going to pay.