A problem with Twitter’s advertising business is that it’s product is used for text-based information (tied to the physical world like work or current events). Users are more engaged and combative on Twitter, making it a poor fit for direct response advertising (users are probably more annoyed by it too).
Contrast that to Instagram, images and short videos that are highly produced to show your best self. Users are taking a break from something else to look at it and the aspirational content makes it a great fit for direct response advertising.
From Twitter Has a New CEO; What About a New Business Model? by Stratechery.