First we have Burnham getting a hold of the Red Angel created by her mother who also did things with it that most likely caused issues in the Temporal War for many years.
Then we have Spocks brother, Sybok, going off on a religious romp across the galaxy looking for God who was nothing more than a malevolent being trapped on a planet by others of his own kind.
Mr Spock, what the h*ll is wrong with your family?
Cuz... "muh drama"?
In seriousness, it's a bit more interesting as well as being directly related to drama (and falls into the trap early-TNG had):
Short edition: Vulcans were also supposed to be a symbolic foil for other characters and each new dysfunctional character related to Sarek and/or Spock starts to dilute that. Humans were supposed to be evolving and moving forward and not "be perfect" I'll also bring up TNG in...
...In the long, sleepy-time inducing edition:
Burnham is part human and raised on Vulcan, or was a human adopted or whatever, the point for her character is that there would be internal conflict to create a more complex character. In concept, I like that as it's novel and a lot of people can conceivably relate to "inner struggles" or whatever the vernacular is.
Also, remember how in the late-80s everyone said "the most human person in the crew is Data" as a backhanded compliment? Everyone being perfect is not dramatically appealing. This also falls into a number of early-TNG stories where people just didn't care because the whole presentation was flat. (TNG found other ways to induce drama and suspense, but "no conflict among the crew" had some viewers balk. )
Sarek's mother was also a Vulcan, which makes things a tad more difficult. Just
why he'd eschew Vulcan teachings, on top of a zillion years of purported evolution... I'd argue that viewers should decide for themselves what might had been since telling a specific answer might be worse than keeping it a mystery.
Another reason is, ever since season 1 TOS, Spock was deemed even more popular than Kirk. Spock is a groovy cash cow, man, don't be such a square! Gag me with a spoon! /crappyslangfromtwooverrateddecades
The worst part is, diminishing returns every time Spock has another cousin wander on in and also happens to be dysfunctional... this falls into "small universe syndrome" too.