Small sites carry a different risk
Large accounts have attention built into them. Somebody visits, somebody reviews, somebody notices when standards move. A small site often has none of that, and the arrangement runs on whether the individual cleaner is conscientious. That works well for years and then stops working when the person changes, with nobody in a position to notice until the difference is obvious and by then the arrangement has already changed shape without anybody deciding to change it.
The other risk is scheduling. When a provider is stretched, the sites that get moved are the small ones with flexible timing, because moving them causes the least immediate complaint. That is a rational decision from their side and an unsatisfactory one from yours. Asking about it during the comparison at least establishes that you are paying attention to the pattern and it lets you raise the point early rather than after the third rescheduled visit.
