Why a particular storage space is not free

A storage unit holds one tenant at any moment. If it is rented on the dates you asked for, it will not appear in the results for them.

A unit on a renewing rental that has not been stopped also occupies the months after its current term. Otherwise the renewal would collide with a new booking, and the sitting tenant would find themselves out.

The search also respects the host's rules: minimum and maximum months, how far in advance you have to book and how far ahead you may book. A unit that does not fit what you asked for simply does not appear, rather than appearing and being refused at the end.