They also held licenses in the AFL before relocating and merging (the Lions were bought out and asset mined by the Brisbane Bears in actuality, but that's an aside), both fully relocated their businesses to their new markets, and hadn't suffered decades of atrophy to their support bases at the time. BTW, the size of their current support bases in Melbourne are totally overblown as well, especially Fitzroy whose traditional fanbase (or what's left of it at least) is significantly more inclined to support the FFC than the Lions if they continue to support in any meaningful sense of the word at all any more.
In other words the Swans and Lions brought something of value to the relationship, namely a license, pro players, and other assets and infrastructure as the case may be, that neither Bears or Jets have.
Perth and Adelaide don't, or rather shouldn't, need to partner with either of them to get a license, and they'd still need to invest in most of those assets and infrastructure anyway as the Bear's and Jet's isn't up to NRL standard anyway. Furthermore, all the genuine benefits that the Bears and Jets offer could be gained by simply affiliating with a lower tier club/clubs in either NSW, Qld, and potentially even NZ or the ACT, without the need to give away ownership, the brand, home games, places on the board, etc, etc.
We haven't even touched on the impacts that being lumped with the Bears or Jets could and would have on Perth and/or Adelaide either, which are significant, but most people whom support these ideas don't seem to give the faintest f**k about that anyway, so it's probably a waste of time.
Nobody in their right mind would agree to partner with the Bears or Jets given their demands and expectations, not unless they felt they were being forced to anyway, and given that it'd be an unforgivable travesty if the NRL pressures either Perth or Adelaide to take on the Bears or Jets just to appease out of touch boomers in Sydney/NSW whom shouldn't be the target audience of either a Perth or Adelaide side in the first place.