Yeah, I just don't get the "this isn't Oblivion/TES" comments. Fallout has always had
spears, yet shields are too much fantasy? Really? Oblivion doesn't even have spears!

Fallout has a mixture of primitive and high-tech equipment. It's part of the charm. There's nothing contradictory to the setting about using a shield.
To me it seems more likely that they didn't want to have to deal with the mechanics of blocking bullets, laser beams, and plasma globs with a shield.
If we have shields in FNV I want a kevlar shield and a high powered rifle with a bayonet. How's that for melee

I like the way you think.