I liked Alien Covenant, and from what I've read, most reviews are actually quite positive.
As for the money it's bringing in: this is no longer just about the box office like it was in the 80s or 90s.
It's a chapter in a long running franchise that makes money on an ongoing basis from lisencing deals, dvd (re)releases, etc. And in order to keep people interested in the merchandise, they revisit the series every so often with a new movie.
I'm sure Alien will continue, regardless of Covenant's final BO result.