Twitter conversion rates are terrible however they do offer something that other platforms don’t or at least not easily and that is sentiment analysis in response to ads and direct engagement.
Retailers, CPGs and other brands as well as many ad agencies and data science companies in the retail use the Twitter APIs to data-mine tweets for analysis often hand in hand with the promotion, ad or engagement campaigns that they or their clients are running.
On other platforms you often only get a binary match with a certain level of confidence to a sale as you can’t easily get what people are talking about.
With Twitter being primarily a public platform you can get much more than has a person bought an item within X hours/days of having an ad served to them.
So the “marketing” spend on Twitter is split often between servings ads and consuming the analytics API, and the latter is used more often however it’s only valuable as long as brands advertise and directly engage with users on the platform.
This is also why advertisers dropping Twitter as a platform is worse than just lost ad revenue since it also harms their only other major revenue stream.