From Elon Musk:
"Twitter was acquired by X Corp both to ensure freedom of speech and as an accelerant for X, the everything app. This is not simply a company renaming itself, but doing the same thing.
The Twitter name made sense when it was just 140 character messages going back and forth – like birds tweeting – but now you can post almost anything, including several hours of video.
In the months to come, we will add comprehensive communications and the ability to conduct your entire financial world. The Twitter name does not make sense in that context, so we must bid adieu to the bird."