Well, the summer tour is mainly a festival tour, with a shortened setlist (90 minutes), and they were aiming for unusual places. Like the shows in norway, where they played one "headlining"-show where Pagan's Mind opened for them (Langesund), and then one up far north where they shared the stage with bands that are not similar to them AT ALL (and which they recieved much negative attention for too, unfortunately) (Tromsø).
https://www.varden.no/kultur/dream-theater-plays-in-a-fishing-village-in-norway-1.1429678But the thing is, and this is something I've noticed over the past few years - the festival circuit is becoming heavily saturated here in Europe. There are so many festivals during the summer. I had a hard time picking out which shows to go to, which festivals (if any) to attend. And honestly, the festival circuit isn't about getting the fans to come. It's about getting exposure towards people that might not know of you. The festival circuit doesn't pay nearly as well as a proper tour does. And I know that DT really liked playing at these weird places that they never got to play otherwise.
DT did peak in popularity a few years ago. They'll probably never reach that level of popularity again. And I don't think it's because of the setlist. I just don't see as much of an influx of younger fans anymore - 10 years ago at gigs there was at least 25% of the attendence filled with kids. Now, these same people may come, but there are no new "kids". The kids that get into prog nowadays tend to go for more "sexy" alternatives like Steven Wilson, Opeth, Haken, etc. You can see it online too.
But, I mean, Mike Portnoy was playing Oslo with the Neal Morse Band on monday. In a 400 person venue. That was sold out only 2 days before the actual concert date. I think July is a harsh month for concerts if you're not Paul McCartney or the like...