Onscreen, we only saw a couple hundred ships. But DIS S2 established that in the 2250s, Starfleet comprised over 7,000 starships; by the 2400s, it should be even larger to match the increased size of the Federation. Now, Matalas has said that calling it "the entire fleet" is just a bit of hyperbole, as starships attached to duties that could absolutely not be compromised on were still out there. But if we assume that the fleet in Earth orbit comprised something like 75-80% of the fleet, then we probably still need to be talking about something in the area of (and I think this probably conservative) 10,000 starships. I can only conclude that those starships were all orbiting at various locations and altitudes and most of them weren't visible to the naked eye from the orbital coordinates that Sol Station, the Enterprise-G, and the Titan-A were near.