Ad revenue went down because of boycott calls by dissatisfied Twitter-users who could not handle the opening of the Overton window. To many that open window was a breath of fresh air but to them it carried in the stench of different ideas which had formerly been filtered out. Many of them made a great show of claiming to leave Twitter and some of them left - they're part of that 15%.

Twitter is still not my thing because I dislike the format which I see as a textual forerunner of the likes of TikTok but it got more palatable after Musk brought in the kitchen sink and started throwing out the old censorious guard.