Ok , time for to to own up.
I've been and still am a fanboy of AMD over Nvidia since , I dunno, 20 years before Nvidia were even around.
But the OP asked for this not to get into the red Vs green thing, so I won't state reasons.
The OP asked specifically why buy Nvidia over AMD so will answer.
Over the years I have purchased 3 Nvidia cards, the rest all AMD.
Nvidia cards were, 8800gt(s?), 1070, 3070.
Reasons:
8800gt(s?) - bracketed the "s" because I genuinely can't remember although I think it's was the GTS because it was REALLY expensive at the time, I'm not sure why I bought this one but just hyped as a great card which I believe it was, mine lasted a year before it failed.....
1070 - (Evga) very good card and I think at the time did outperform the AMD equivalent but a fair margin, good amount of VRAM for a change from Nvidia, still being used today in another system.
3070 - The ONLY reason I bought this over the AMD equivalent is I really wanted some better FPS for PUBG, and unfortunately this was in the middle of the mining thing, OCUK were doing their forum members deals so managed to pick one up for (at the time) a very good price, however had a 6700xt been available for some price, I would have quite happily picked up one of those instead.
If I were buying a new card today it would be AMD I think they have a good lineup and better bang for buck, but I just don't need an upgrade at the moment.