As others noted on the runway, that must have been a feat to take it out to the runway, on the Tarmac but left stranded, likely, I could see how that could happen more often than redirect / lost luggage in the last minute hustle/load, but on a regional should be a system there.
If in 18 years only lost luggage once and 1K that is pretty darn good record.
I would say what would upset me more is it took "several" days, as a 1K I'd expect the bag on the next flight or there by next AM for such a mistake, but again like you said, it's UA so customer first service is lacking as a corporate cultural.
Like you I fly UA as for where I go little other choice, but if the competitors offered similar schedule/flexibility I'd not even be flying them!