BoG and RoF were canon, too. Even Yo! Son Goku and His Friends Return was considered one.
And we know how they all ended... first two diluted and caricatured, Yo! completely ignored and forgotten.
I wish I had your enthusiasm, Galan. Sure, essentially you're right, but it ain't over till the fat lady sings...
BoG and RoF are still canon stories -- they were just retold in the anime. IF we get an anime retelling of the Broly film, the same will hold true. Either way, DBS Broly is still very much a canon character.
Yo! is still canon as well(even if has been primarily ignored.) Tarble was recently referenced in a bio, in fact. 👆
Toriyama himself said the original Movies are meant to take place in an alternate reality, apart from his mainstream/manga canon:
What is your personal stance on Dragon Ball's theatrical films, Sensei?Toriyama:
"I take the movies as 'stories in a different dimension from the main story of the comic'. I'm entirely just an audience member for them."
ie. They're essentially non-canon for the same reason the DBZ anime filler scenes and GT are non-canon: Toriyama had almost nothing to do with them. They are purely Toei creations.
The difference is that Toriyama IS directly involved with the DBS anime's creation. He provides Toei with a rough script/outline for each major arc and gives them the general direction he wants the story to go, but still allows them to have the creative freedom to expand on the plot how they see fit.
That being said, the DBS manga does, technically, represent a truer look at Toriyama's actual vision, because he is much more involved with its creation from start to finish -- he discusses in great detail each and every part of the plot with Toyotaro, and always proofreads/edits Toyotaro's work before it is finalized. That's why you see differences between the anime and manga: one has Toei influence, the other does not.
Regardless, both are canon to the franchise.