Meh, canon is overrated. The big draws of shipping to me are the fanart, fanfiction, etc. and two characters don't need to actually be in love for stuff like that.
The thing that attracts me to Pearlshipping is how well Satoshi and Hikari work together just as strictly platonic friends as they would if they were love interests. They clearly don't see each other as anything more than friends in canon, but they were also close enough that it's not hard to create something romantic out of them (ex. the episode where they trained Glion). Of all the "Satoshi/main girl" pairings, I find Pearlshipping to easily be the most believable, even if Satoshi and Hikari don't actually feel anything romantic for each other. Amourshipping works only as a one-sided pairing (IMHO; granted, it can work really well like that - it's the only other "Satoshi/main girl" pairing I like), I could never see anything that would bring Satoshi to like Haruka or Iris or vice vera, so I can't really buy into Advanceshipping or Negaishipping, and I just don't care for Pokéshipping.
That was only because of a few reasons:
1) During AG we weren't exactly sure if Misty was gone for good yet. Also Misty still made cameos in AG (unlike every following series) so Pokeshippers still had some things to cling to
2) Advanceshipping was the first big alternate ship to Pokeshipping, and a lot of male fans latched onto it. At the time we also didn't know May was going to leave after one generation, so it seemed like a bigger deal back than compared to now.
3) Contestshipping started to get really blatant toward late Hoenn and Battle Frontier, so we had a huge ship that essentially rivaled Advanceshipping. No other female companion had two huge popular ships like May did again.
I dunno. I feel like Pearlshipping and Ikarishipping could be right up there with both of those, but that's just me.
In any case, you pretty much nailed why I got into Advanceshipping during that time. For someone who didn't care for Kasumi or Pokéshipping (and still doesn't) and wanted a potential Satoshi pairing that didn't involve either her or Shigeru, Advanceshipping was a much-appreciated alternative. Plus, the relationship between Satoshi and Haruka was new and fresh and I preferred it to Satoshi and Kasumi's. But I started losing interest near the end of the Battle Frontier.
By the time DP started and we realized the formula of the show, a lot of the shipping wars died down. People paired Dawn with virtually everyone, Ash, Zoey, Kenny, Paul, Conway, Gary...etc. and nobody really cared. Misty never appeared in DP so Pokeshipping had nothing really new or anything to talk about. We saw May's rivals in the Wallace Cup but that was also it.
This is true. But even without the shipping wars or a major pairing like Pokéshipping or Contestshipping that had hints to back it up, I feel like DP was a high point for the anime's shipping fandom in general for the reason you just mentioned. The greater amount of recurring characters meant a greater variety of pairings. Pearlshipping, Ikarishipping, Penguinshipping, Appealshipping, Comashipping, HeatTagShipping, Cavaliershipping (this is the Hikari-Shigeru one, right?), Morpheusshipping, SapphirePearlshipping, FireRedShipping, Againstshipping... in addition to the older stuff like Pokéshipping, Contestshipping, Advanceshipping, and Palletshipping. There were a lot of pairings coming out of there, and I remember a few of them actually having a decent amount of support.
Its actually kind of funny in retrospect that when DP began people thought Misty was going to appear and meet Dawn, or that Pearlshipping was becoming a big thing. Very silly looking back on all of it now.
In Kasumi's case, I can understand why. She did make a few AG appearances, briefly showed up in one of the DP openings, and the writers did bring Shigeru back so it wasn't impossible. People still thinking she's going to make some kind of grand anime appearance
now (as opposed to maybe getting an episode or two for nostalgia's sake and then disappearing again) are really kidding themselves, though.