Not sure why you've been downvoted, you've called out the most likely concern. Despite the APIs bringing in some money, I doubt they've covered the ad revenue

Not sure why you've been downvoted, you've called out the most likely concern. Despite the APIs bringing in some money, I doubt they've covered the ad revenue loss, especially in recent years as more and more advertisers started using Twitter at scale, and as more of the world joined Twitter. The audience using these APIs via Tweetbot, Twitterific, etc, has become an ever smaller percentage of Twitter's userbase. It's probably not even worth the effort to figure out how to better monetize the APIs, given the small audience. And not everyone is so desperate to avoid the algo timeline that they're willing to pay a 3rd party app. Personally, I was a Tweetbot user from around 2013 to 2018, but I kept switching over to the first party app more and more, as Twitter started to add more features that weren't available to Tweetbot. And then I discovered I was spending all my time in the first party app anyway because of the algo timeline, so I quit using Tweetbot.