They do make good horror movies! The problem is they've all been used...
Purge, Insidious, Happy Death Day, Ouija, and Sinister are all solid, maze-ready properties. All but one has been used.
The other great films they have made - Split, Get Out, Paranormal Activity, Oculus, Hush - are all either not maze-ready or not controlled by Universal.
They do occasionally put out turds, like any studio. It just so happens that these particular turds were very financially successful.