Neither is Deadpool or The Dark Knight but they still made more. Being family friendly does not have much to do with it imo. There is a huge audience for this stuff. X-Men has never had a flop even with it's mediocre films, so that alone speaks alot.
Imo the answer for why it can't see a huge increase will always be that they don't use the majority of their characters or elements to the truest marketable potential. It took 14 years to get to Sentinels, we had a bad Phonix film etc. Too many characters are not walking out of these films as marketable franchise stars or engaging/fun characters. Lately Characters like Quicksilver and NTW have had a far bigger audience reaction then main X-Men. They are just more fun then characters like Rogue and Iceman in the films. Downplay the fun characteristics of them and they lose their appeal.
For example, just having Deadpool show up like in XMOW isn't enough to grab audiences, you need to capture why he was popular and worked as a character in the first place. So if a character like Storm or Cyclops is represented stronger in Apocalypse more so then the OT then they will surge and help the franchise become more profitable. Likewise with just about any character.