Perhaps the homeowner doesn’t permit early check in (some don’t) or maybe previous week guests have late check out...it could be any # of things. Things you will probably never discover. If it’s a really big home, cleaning could take more time that a smaller home. I do agree that there may not be enough cleaners to handle the seasonal cleanings. It’s a lot to accomplish in a short time period. But then, there are also less than enough housing facilities for cleaning staff on island that are reasonable, which may contribute to the lack of staff.
Just stop thinking about it. Maybe you’ll get lucky and home will be ready when you arrive.
For your doggy, and family, some restaurants that have outside seating allow dogs. IIRC, Good Winds in Rodanthe does,and even bringsa waterbowl for pooch. Then you don’t even have to prepare a meal that night.
I most sincerely hope you have a wonderful vacation.