Look at it like this:

The Rizzutos were powerful, but still very small as an actual family. They seem to be essentially wiped out now. I mean, they still exist at a small level but they no longer have a monopoly on Montreal. That monopoly is long gone, there's likely multiple mob groups (maybe 2-3 at least) now in Montreal doing their own thing independent of each other.

The Bonannos, for as much as they got hurt by Massino and Vitale flipping, are still in power and a viable family. Like I'm sure the FBI knows who all of the captains and most of the soldiers are, and has a decent idea of the structure. Obviously they don't have a monopoly because there's five families, and they'll never be as strong as they were back then, but the family's hierarchy still exists.

The Rizzuto's hierarchy / family structure seems broken. The people who have more power in Montreal now likely don't give a shit about joining the "Rizzuto Family" or whatever. Montreal at their peak seemed far closer to a confederation of different drug trafficking groups than a traditional LCN family.