I tend to believe that the 1st, 4th, and 8th fleet either were deployed at other fronts, or served other roles. This includes defensive purposes (possibly first fleet defending major diplomatic stations), escort services, patrol services, medical services, and communication services. We might not have heard about them as much because they were smaller fleet with established supportive roles. Additionally, these fleets may also be smaller tactical fleets, designed for hit and run missions, which would make then less than optimal to include in major battles.
For example, the 10th fleet was charged with protecting Betazed and it's outer colonies, but was caught off guard on a training mission. The fleet itself might not have been that big. Perhaps 20-50 ships designed to protect Betazed, in addition to neighboring systems like Andor and Tellar. If the 10th fleet was solely responsible for defending Betazed, then perhaps these other unmentioned fleets were defending Andor and Tellar.