Well, Shin Godzilla is the highest grossing Toho Godzilla film. It made 78 million worldwide, with 70 million of that coming from Japan. Before that, the previous Toho Godzilla, Final Wars (which was a big 50th anniversary film) made around 22 million. The film prior to that, Tokyo SOS, did around 12 million, which was roughly on par with the previous movies. None of these films really perform internationally.
Godzilla 2014 and Godzilla King of the Monsters made 30 million and 37 million respectively in Japan, which went to Toho.
Now, they’ve said before that the agreement between Legendary and Toho is, both can make Godzilla films, but they can’t release in the same year. Also, Toho gets a level of input in how the Kaiju are depicted in the Legendary films; they have approval of the final designs, and they give notes as to how they think the kaiju’s personalities should come across.
Just looking at the numbers there, it’s a pretty good deal for all involved. Toho basically takes in a higher profit than they normally would, with little personal cost, plus they get to continue their own creative efforts mostly unabated. This is a situation where they’d be throwing money away if they didn’t try and continue the agreement.