When feeling down or depressed, that's about the last time you want sit with your thoughts or practice loving-kindness.
So the negativity easily makes more of itself, and you're along for the ride.
I used to have a big problem with being promiscuous, and lots of negative thinking and guilt with it.
What helped was noticing the thoughts always stayed about the same.
I cut off harmful relationships and established a lot more balance over the years.
But it didn't matter one bit! Same old self-hating thoughts, like nothing had changed.
One night I suddenly thought, "Wow! Why am I still listening to this? It's not remotely accurate."
I never noticed my thoughts could be total fiction, especially such old and forceful ones.
Until you find some crack in the story, it may be hard to see beyond the intellectual level you mentioned that a thought is still a thought, no matter the content.
It's just too magnetic, the habits too familiar.
It may be a "says who?" moment, or deciding to welcome the negativity as fuel for compassion practice, or as subject matter to study how cycles of thoughts arise, or to see what negativity feels like physically, or...
You have many options that don't include tuning out as though watching TV at the airport just because it's there
And anyway, falling on your face and getting back up is 99% of the path. You just fall less as time goes on and you learn where your feet are