Not totally surprising - at that time of day, there are few international flights where AA elites (EXP/PPro) would be eligible for SoHo (the 8am BA to LHR and maybe 9am CX to HKG). [Not sure if there's something to the Caribbean or Mexico that would qualify?] Of course non-AA/AS OneWorld Emeralds are eligible for Soho on all flights, but there probably aren't tons of them. AA elites flying to LAX/SFO would only be allowed in Greenwich (J) or be directed to Chelsea (F)*; no status-based lounge entry on those routes. Obviously by late afternoon you have a lot more international flights which significantly increases the pool of passengers potentially eligible to enter SoHo.

*Of course F pax could choose to use Soho.