You're acting like he hasn't had public outbursts before...
Ya know.
"George Bush doesn't care about Black People".
"Taylor, I'ma let you finish..."
MBDTF came out in 2010. That was around the beginning of social media entering the mainstream (Kanye joined Twitter in July 2010).
So up until MBDTF, he didn't have a device in his pocket that allowed him to broadcast his unfiltered thoughts to millions of people. Up until that point, his public image was likely carefully managed by his label and management. All of his interviews were probably overseen by them. They likely only allowed interviews where he was asked pre-approved questions and gave canned answers. If he went too far off script, his label likely stepped in.
It's clear now that he has a lot more freedom with handling his own image. He's been signed to his own label since 2016 which probably afforded him a lot more power over his career. He had a few moments prior to 2016 but he didn't really go off the deep until 2017.
TLDR: what you saw as stable behavior prior to 2017 or so was probably the result of a curated image created by his label and management.