Dude, if you're not going to read what I am writing then there is no real point in discussing it.
Sampras played in an era when one surface was highly suited to his game (grass) two less so, and a fourth completely hostile to it (clay). Nowadays all surfaces pretty much suit all players. There are some differences but they are pretty minimal by comparison. Additionally the nature of the modern game (defensive-oriented) discourages upsets. It's a much better situation to be the top player in.
It doesn't take a rocket scientist to work out that if you were the Tour's dominant player for a year in the 80s or 90s, you were a contender for less titles in that period than if you are the Tour's dominant player for a year in the 2010s. That is going to result in the top players accumulating more slams.
I am not sure what is so difficult to understand about that.
I wouldn't call the differences minimal. If they were minimal, then the GS wins of Federer, Nadal and Djokovic would be much more evenly spread across all four events than they are.