This is just the way the market, and music industry as a whole, has gone.
In terms of attendances Italy surely is an exception, but I can tell you that all post MP era shows I've attended (but one) were either sold out or very close to be. And for me personally nowhere less exciting than those I've attended previously (not even TA one)
Which is something I can't say, for example, about the PN09 tour.
But then again, numbers are valid only if put into context.
DT has dropped in popularity? Yes, as it has metal music in general
DT concerts are less attended? Yes, again, in proportion to how concerts (and this kind of music) has gone lately
Is popularity determined to how much a band speaks to its public?
Sometimes, and of course DT is a good example of that, but in 2017 it's not about how many things you do, but how these things are done.
In all honesty, and I don't know if you can blame someone for that, but the only thing I really feel like it has changed the way I look at them is that somehow they've really regress in terms of maturity: they used to be cool, to write very interesting arrangements, to write deep lyrics (e.g. Voices) ecc...
And then they did SC and never fully recover from that.
I like what they've done since MP has departed, I really do (way more than last 2 MP era albums) but do I fell as engaged as I use to be until SDOIT? Not really.