I'm a VRBO homeowner; our beach home is located on Holden Beach. The homeowners can decide when, how long, and/or if they want to rent to an individual.(VRBO- Vacation Rentals By Owners)
I personally abide by what I have on my vrbo page, because it wastes my time and prospective renters' time, if I don't. Our policy for off season (we set Memorial Day weekend as the beginning of our home's in- season) is that we will consider rentals for less than a week. ("consider" being the pivotal word.)
This year, more than the previous year, I've had more people interested in week-long rentals in May and early June. At this time, I have 1 week rented in April, 2 weeks rented in May, 3 weeks rented in June, all of July, 1 week in August, 1 week in Sept., 1 in Oct. and 1 in November. This time last year I only had 2 weeks for the entire year spoken for...I'm now receiving 5-10 inquires most days since early January. .
Right now I'm not considering anything less than a week from the first of May through the end of October. If a week remains un-rented within 2-3 weeks of the date, then I would "consider" a last minute, less than a week rental...I may also decide to use the home myself. I think most VRBO homeowners have similar policies.
I would think the homeowners you sent the inquiry to are having similar experiences, and at this early date when so many people are still planning their vacations, they don't want to settle for a partial week rental, when they possibly could get a week-long rental. It's business; nothing personal.
You may need to consider hotels/motels or wait until closer to your dates to try to find a "last minute", less than a week rental.
Best Wishes.