6000 tweets is only for people with Twitter Blue, and it counts scrolling past a series of tweets on your timeline as reading them, so it's really easy to hit that limit even as a paying bootlicker.
For those of us sane enough to not spend any money on that godforsaken platform, it's only 600 tweets, which is disgustingly easy to hit. Scroll a little through your timeline, open a few tweets to read replies, and you've hit your limit in less than 30 minutes.