Keep in mind there are times when black shoes are the appropriate choice with a navy suit. If I'm going out at night in my navy suit, I often reach for my black cap toes. There are also occasions in the business world where the occasion calls for black shoes with a navy suit. There are certain hearings or meetings where I would feel uncomfortable attending in brown shoes.
The above two are correct that the general consensus for conservative business dress is black shoes with Navy suit.
Can someone please explain to me the thought process behind having fewer black dress shoes compared to shades of brown? I only have one black dress pant so it's not like I wear a lot of black but I do like wearing black dress shoes with my navy and grey pants. Just feel like pairing some black Westchesters or Rutledge with a nice pair of slacks and a tie looks good. Am I missing something?
I think the idea is that, just like white dress shirts, black shoes should only be worn in formal settings, i.e., with a suit. That is the reason I would not wear black shoes with grey pants. I definitely would not wear with navy as I try not to wear navy and black together and brown and black together.
Regarding your last comment, the general consensus in Men's Clothing on SF is that if you wear a tie you must be wearing some sort of jacket. Some may find a sweater over a tie with no jacket acceptable.