Why? They're filming the 4th season now - so IMO better to just okay the 5th so the Writers room (which they feel has been good for the run of the series) stays together and they get full use out of the Canadian studio before maybe the shit hits the fan WRT the merger.Surprised they publicly announced it would be ending so soon.
It also preps the hard core fans and maybe even makes them be sure to tune into all the 26 remaining episodes.
TLDR: There's really zero downside and if PICARD and Discovery are any indication, a marketing upside.