Oh boy, I’m never going to be able to forget this plot hole now.
Sorry.
It’s fine. Ghosty Luke likely knew future events and saw that this was the easiest way to permanently destroy Palpatine. If neither Rey nor Ben showed up, who knows what shenanigans he would have done during the battle and after. He could probably drain all the troops that tried to attack him and escape somehow.
At least that’s my head canon answer.