Elon Musk himself hit his own rate limits... while reading people's replies about rate limits. I believe current limits are 500 (unverified) and 1000 (verified).
ChatGPT is fueled by downloading everything on Twitter, Reddit, and other websites. I suspect ChatGPT and other AI bots are increasing the amount of downloading ("scraping"). That in turn increases Twitter's costs (bandwidth, and more servers to handle more traffic)... but how does ChatGPT benefit Twitter? I think the lack of benefit, versus rising cost, is why Twitter is imposing rate limits. I know Reddit is also taking action, but I haven't followed that closely (and some areas are protesting, so the outcome remains to be seen).