It happens that a sitter doesn't respond when you are out of her/his radius, or the sitter is not available the time you selected, or doesn't accept the kind of pets you own, or they are unable to respond for personal reasons.
It happens with clients that they ask about services the sitter is NOT offering, or they are confused about services - for example the sitter is offering boarding only, but the client is asking if she can make an exception and would house sit. Or they are only boarding small dogs, yet the client with his 100 lbs dogs is asking them to make an exception... etc...
I am not saying this is the case, but just some examples when sitters just don't bother responding, because many potential clients refuse to read their complete profile before asking to book with them.
Oh also, there's sitters out there who no longer provide services but never deactivated their profile and left the calendar open for the rest of the year, and then it seems they are available but they never check this site anymore. In that case you can call the customer service and ask them to check if the sitter has been active lately, since you are dead set on this 1 particular sitter. The customer service can help you.
If they’re a good rover sitter, it should be within an hour or less! I pride myself in making sure to respond to owners right away or as soon as I can when a request comes in. Rover recommends reaching out to a few sitters at a time. Good luck!