At the time, many people didn't realize that Android + iOS shipments had dwarfed Wintel shipments until they saw this dramatic image in her 2012 slide deck. https://image.slidesharecdn.com/internettrendsstanford120312...
Since then, IMO, people keep showing up because they're looking for another major shock. But there hasn't been a major shock like the rise of mobile since then. Mobile is still big. China is still big. etc.
Now her presentations convey a feeling of comfort. "I believed all of this already, because I am a smart, well-informed person, and here's the data to prove it."
Let's say I'm wondering about "number of smartphone users growth". A google search might pull one chart for that.[1]
What Mary Meeker does is ask 200 of those types of questions, gathers all the data to make the charts, and puts them together in one deck. That's more convenient than conducting 200 searches on the Statista website.
I think the disconnect and dissatisfaction happens because they expect Mary Meeker's slides to provide some mind-blowing insight. I think it's more realistic just to accept it as a nice data dump of some of the latest trends.
[1] https://www.statista.com/statistics/330695/number-of-smartph...
It's well researched, it's sourced, it's free - quite likely the only compendium of that size that meets those criteria.