Rebrands of well known consumer companies are *very* expensive and time consuming. A company known globally which is reasonably well regarded will incur high costs in recapturing the brand recognition and perception of the company by people.
Yes there is grief from Easygroup, but is it sufficient to really go for the complete rename option ? Perhaps the game for Easygroup is to extract as much cash as possible over a long term timescale without being seen as sufficiently awkward to push Easyjet management too far.