There's no rule that says the person who wins the most has to be the most popular. Federer and Nadal have always been more likeable than Djokovic. It's not that complicated.
Also, Switzerland is a spectacularly beautiful country. I've seen a bunch of tourism videos and I've never seen one with Federer.
I believe Djokovic is the GOAT. But I also recognize that in Roger and Nole's case, there are people who make a distinction between BOAT (best ever) and GOAT (greatest ever). I think it is impossible to argue against the former and I would not argue against the latter, either. The evidence is now overwhelming, and it was already evident before Nole's latest GS victory.
However, for a chunk of fans, sports fans in general for the most part rather than specifically tennis fans, Roger will remain greatest in their estimation. Their definition of greatness is broader than just wins on a tennis court, I've talked with friends of mine who hold this belief. They usually mention some combination of the following that they think supports Roger's greatness in tennis history as opposed to Nole's:
Contributions to growing the game
Public demeanor and bearing
International impact and recognition
Level of engagement in his career
Aesthetic purity of performance
Spirit of camaraderie generated
Pure likeability and general sportsmanship
Got there first
I'm not unsympathetic to the point of view that greatness relates to more than just pure athletic achievement; I just don't agree with it in this case. That being said, I do think distinctions can be drawn between "best" and "greatest" in sports arguments. They are kind of fun, actually.
On the Swiss tourism viewership thing, Roger clearly makes an enormous difference. I compared Roger's three top Swiss tourism videos to the three highest viewed that I could find without Roger in them. Here's the rounded-off results:
Roger Swiss tourism videos: 238 million
Non-Roger Swiss tourism videos: 8 million
Beautiful as Switzerland is, that is a humongous difference.