I actually found myself getting frustrated with all the weapons in the original Bioshock. There were just too many and too many damned types of ammo to keep track of, and I would often waste precious seconds in battle just fumbling around for the right weapon. Between that and choosing all the damned plasmids I sometimes felt like I was playing wheel of fortune more often than a FPS.
So while I sometimes was frustrated with having to choose in Infinite[footnote]Though over time the decision-making became easier as I favored certain weapons when upgrading. And when I got the hand cannon that became my default sidearm for the rest of the game, so from that point on it was just a matter of stocking the secondary weapon with more kick, like the RPG or machine gun.[/footnote], I liked it during battle because it was one choice made easier. Plus, as others have pointed out, it forces you to think about and rely upon the vigors more. You couldn't just unload all your special ammo in all your weapons to take down a big baddie like in Bioshock--you really had to think about what you were fighting, what its weaknesses were, and what plasmids AND attacks best suit the situation.
As for why they did it, I really don't think the "realism" argument holds water, considering you can run around eating everything you find like a madman and never suffer any consequences for it (except maybe if you ate something rotten). I think they did it to balance the battle system, again so that you're forced to think about the plasmids vigors more and use them all to your advantage.