There are several things that separate the NYI/NJD/NYR situation from TOR/HAM but two in particular:
1--- The circumstances that dictated the Islanders founding and Rockies' relocating (as laid out by
@KevFu) were completely unique to the era. If not for the WHA, it's entirely possible the Isles aren't even founded (and the Rangers opposed the idea at first, at that). The Leafs were owned by Harold Ballard at the time and he had an entirely different way of dealing with the "spectre" of the WHA, which was to purposely make the Ottawa Nationals' move to the city as cumbersome as possible. If the Rangers' owners had been as cantankerous as Ballard and treated the Raiders/Golden Blades in the same manner, you probably never see the Islanders. And the Devils did in fact come with territorial fees to not just one but
three teams (also the Flyers), which John McMullen either on accident or through savvy realized would be a bargain compared to what the future would bring.
Those circumstances will never re-present themselves. I think the 1970s or early 1980s would have been a great time for Hamilton or the GTA in general to get a 2nd team but Harold Ballard was too unpredictable and irascible for it to occur.
2--- The big thing with 2024 circumstances is that the Leafs aren't just hard to persuade because it's "their territory." They're hard to persuade because of
all of the other sports interests they have in the city. Including minor league teams, they own
seven pro teams in the area. They like having all of that (I'm convinced they'd hold a ticker tape parade if the Jays ever left, not that they're much of a threat in terms of interest right this second...). The profile of hockey in the GTA is right where they want it.....the last thing they'd want is a second NHL team taking attention away from the Raptors, etc.