>why?
You are apparently not understanding how the ADS-B Exchange network works.
Read:
https://adsbexchange.com/faq/
Understand:
https://www.adsbexchange.com/coverage-map/
It's not some all seeing eye in the sky with wall to wall global coverage. What you call buzzing around and going back was simply the aircraft flying outside the range of network receivers. He was off coverage for about four hours. During that time he landed. Then took off for the return flight. All you have to do is put the call sign into flight aware to get the rest of the story on Jet Blue 2784.
https://globe.adsbexchange.com/?icao=a874e1