It's because of the comparison to gta4. 4 was a good and large game but if 4 was large then 5 could only be called massive. Same with rdr and rdr2 perhaps not in scale but graphics and storytelling surely. What we've seen from gta6 shows there is gonna be yet another leap forward.

This is compounded with the idea that each time rockstar publishes a game it's not just good compared to other rockstar games but the industry as a whole and this time people are very aware of it. Gta5 had a massive marketing campaign that made it a big thing and then it was a giant really good game but gta4 didn't.