I've never understood why Perth Glory had bigger crowds in the NSL than the AL? It makes a lot of sense to Perth residents, but nobody else outside WA.
A few factors in play here;
NSL era (1996-2002)
* During the NSL era both WA AFL sides were bad. Fremantle never made finals in this time, and the Eagles were solidly "mid-table"; might make finals but would be eliminated after 1 or at most 2 matches without ever looking like serious contenders. Unlike the AFL teams, you could go to a Glory match and be fairly confident of seeing a win. Suspect there were a few Glory hunters in the crowd during this period (pardon the pun).
* Glory were a bright, shiny new WA team. Hell, even Channel 7 here in Perth ran a half hour "Glory Days" TV program. Try to imagine that today!
* Glory had a fair amount of local talent (much like the Eagles in the 80's)
* The atmosphere in the shed was something that hadn't been encountered in WA sports before (at least not to that degree)
* Meaning no disrespect to the other NSL teams, but most of them were of a much lower standard than the Glory. IIRC, the Glory never had an NSL season with more losses than wins.
* The NSL was a larger league; 13-16 teams during the Glory's time.
* Kinda worth mentioning; Glory did get good crowds in the NSL, but they weren't
that amazing. The averages over an entire season was probably only 10-11K. People tend to remember the large crowds (eg 45K in the 2000 Grand Final, or 18K against South Melbourne in a league match), but there were plenty of matches with crowds around the 7-8K mark, which seemed big compared to the crowds of most of the other NSL teams.
A-League era;
* The 18 month off-period between the NSL & A-League probably hurt the Glory more than other teams, as it killed the momentum they had from their NSL victories.
* When the A-League resumed Eagles were back to being strong (finalists in 2005, premiers in 2006)
* The Glory was no longer head-and-shoulders above 90% of the other teams in the league.
* The shed atmosphere had been diluted somewhat. Although the shed is open on 3 sides, with just a wall at the back, WA's Health Department bought in OH&S rules regarding numbers allowed in shed (and possibly a restriction on Under-18s in the shed?) despite the shed not being a crush risk. I'm sure it's just a co-incidence that Neale Fong, the person in charge of the Health Department also worked for the West Coast Eagles at the same time.
* The new A-League was a much smaller league. Only 7 teams in the league for the first 4 years.
If the Glory could go back to getting results like they did in the 2018/19 season (the only season their average crowd was > than the A-League average) for a sustained period of a few seasons, and also if the Eagles/Dockers were bad like... well, like they are ATM to be honest... you'd see the average crowds back up to the 13-14k mark.