I think there is a huge difference between people who travel. There are the "true" travellers who often travel long-term and really want to experience a place, and there are the people travelling with a tourist-mindset with, a bucket list, little time and a huge demand for the same level of comfort which they have at home. The latter are the ones that often complain :D
There was this Indian guy who was in my hiking group knew Machu Picchu from an Indian music video that is called "Kilimanjaro", you have to watch it :D
Unless Kilimanjaro has a different meaning in Hindi, one wonders how many fellow music fans have flocked to Tanzania and been surprised by how different the backdrop appeared?
To my original comment, perhaps @intrepidphotos is right, and it is just a sad reality of our times?
I've always anticipated the complaints and gripes of tourists, but when I first started travelling back in the 1980's, the fellow long-term travellers I'd meet along the way were all generally positive and fun to hang-out with. Not only that, but pre-internet, if you wanted to know what was ahead of you on the road, then fellow travellers were the only people you could ask and share information with. It was a community of strangers, who helped each other to keep moving forwards.
My current journey is about to enter its tenth year, but many of the long-term travellers I meet today appear to have adopted the tourist trait of complaining, to the point where I'll now go out of my way to avoid spending time with them.
Personally, I think the change in attitude I've witnessed can be summed up in one technical invention, the Selfie Stick. Even ten years ago, fellow travellers were the only true source of information vital to the next stage of your journey. Travellers travelled for themselves, because they wanted to learn and grow as individuals, but today, perhaps, it's more about using the Selfie Stick to grow their social media audience? .......... just a thought.
Travelling has become so easy and common that a lot of people are travelling now who wouldn't have travelled some decades ago. My Chinese teacher (who is from China but now lives in Germany) is always making fun of the Asian tourists who are travelling to Europe primarily as a status symbol to be able to post photos on social media, I think you do have a point with your selfie stick argument...
Maybe the internet is part of the problem as well. Some people are planning everything in advance and have seen dozens of photos and reviews of their accommodation and the places they plan to visit before they get there, so of course, they have certain expectations and are not open-minded at all.
I had an amazing time when travelling without any wifi-device for months and think that travelling is all about the experience and not planning ahead. After all, I think that not the travellers have changed, but there are more people travelling now who don't have a traveller's mindset.