Canon is misnomer in these circumstances anyway. Continuity is the more appropriate term, unless we want to devalue "canon" of its meaning.
The word originally referred to the canon of scripture. That is, a collection of writings, inspired, don't contradict(there's your continuity)each other, and written by those who the writing is attributed to, as opposed to a pseudopigraphical work(not written by the real person whom the book is said to be written by.) or apocryphal (which are not considered inspired works, but have historical value)
"Canon" has other additional meanings in religion, but they don't change the original meaning.
Canon Law (which is very similar to "canon of scripture")also needs continuity. It's important that laws don't contradict each other, or if they do, to know which law has precedence.
Trek has no real continuity except in varyingly broad strokes. This is largely not by accident, the expectation of that continuity is externally imposed and for the most part hasn't been a driving factor in the storytelling.
By overstating your case, you only diminish it. Star Trek has followed the following types of continuity:
Continuity of Characters: The characters in the original series continue on to the movies, and appear in the following series. They are also occasionally mentioned in the other series. Likewise for further crossover between the later series. Even Enterprise does this a lot.
Continuity of Setting: The Federation, it's laws and treaties, Starfleet, etc, have a continuity.
-Continuity of time, and dates
-Continuity of Technology
-Continuity of Aesthetics
All of Star Trek TV shows have followed a continuity of story, with a lot of crossover elements between films and movies. They create a fictional universe that feels real, even if implausible at times. Having a continuity gets one more invested, and the pay off is larger.