Although POTC is still a large franchise, it's a good size smaller in comparison to what Star Wars rakes in - the last POTC film grossed ~$241 million domestically, while Star Wars VII grossed ~$936 million.
Similarly, the Avengers film have crossed anywhere from $459 million for Ultron, to $623 million for the first. Although still several years away, you can also assume that the final "Avengers" film will gross similar numbers. Guardians made ~353
Basically, Pirates and Guardians are going to make a ton of money - but likely won't hit Star Wars/Avengers numbers this cycle, and Disney might be wise to separate these "trilogy ending" films