I would suppose it’d be because they didn’t have the connection to the old games. I appreciate the modern Fallouts and Fallout 1 and 2 in different ways. But I can appreciate them all (except for 4 and PoS).
For a lot of people on this site, Fallout classic as we’ll call it and its meticulously researched lore were what they started with; so they feel a greater connection to the older games not only because they’re arguably objectively better, but because you never forget your first Fallout.
For people like me, whose first was 3 and favorite is NV, that same sentimental feeling comes into play with the newer games, even if Beth fucking ruined the lore and punishing gameplay.
I like Bram Stoker and Mary Shelly, but I also like Peter Cushing. It's way easier to do if you're invested in the ripoff before you're invested in the original.