Why?
Canon means "official material"...
Hence the personal in personal canon.
Nobody's claiming any "officialness".
^Anyone else spot in contradiction in terms here?
Anyway, "canon" does not mean "official material" in this context because "official material" covers anything produced under licence from the rights holders. That could include literally anything from novels, trading card, to shot glasses, bath towels, LEGO video games and monopoly sets.
No, what canon means is that a thing described *happened* in a given continuity and that subsequent instalments must abide by this (in theory.) I don't think anyone would claim that the LEGO Star Wars games are in the same continuity as 'The Force Awakens' despite being produced under an official licence and still sold to this day. Now the 'Star Wars: Rebels' series is canon because Disney/Lucasfilm says so and no other reason.