Who is this "everybody"?
There's a lot of better games out there.
New Vegas is better than F1 in every way.
Everybody as in almost every RPG after Fallout is affected by it. All the open-world RPGs. All the RPGs with social elements. Switching Choice & Consequnce from good/evil dichotomy to web of decisions. Games like Morrowind or Knights of the Old Republic are almost more like Fallout than previous games of the series. Plus we have a disproportional number of postapocalyptic games.
I would agree there are better games to play today. New Vegas might be better in *most* ways than Fallout 1 but it brings unique problems Fallout 1 never had and those problems might be more noticeable than its advantages. Of course it features better UI and graphics, but it also has bigger problem. You expect more from a world that you can observe in detail from first person. That's why people might prefer Tetris to any and all games - it's perfect, it has no flaws.
I think Divinity Original Sin 2 would be a stronger case, but maybe it's too fresh to judge. And even then Fallout 1 has an advantage of being the first of its kind, genre-defining RPG.