I personally use it because of how many comrades I follow, I wish they were on here but it is what it is. I assume they’re on Twitter because they don’t know of any alternative and the wide reach they can have.
I use it for some of my other more mundane interests still (music and cooking stuff predominantly), but not politics. Trying to be a leftist on twitter is a special kind of futile. I don't actually post much of anything on it, but there are some good recipe and music resources I keep an eye on from time to time, it remains decent for that.