J.A.R.V.I.S. is the AI built by Tony Stark as an aid & house-help (Butler) based on Jarvis who was the aid & house-help (Butler) of Howard Stark, Tony's father.
J.A.R.V.I.S. is voiced by Paul Bettany & Jarvis is played by James D'Arcy.
Iron Man came out first & then a few years later, Agent Carter came out.
So the question can be either why Paul Bettany, who voiced J.A.R.V.I.S., didn't play Jarvis in Agent Carter or why James D'Arcy didn't voice J.A.R.V.I.S. in Iron Man & subsequent films.
Their (Jarvis's) mannerisms are very similar so from a sense of continuity why didn't MCU producers hire the same actor to play both roles. A word from producers would be great.
there is no actual problem to be solved: “I’m curious if other people feel like I do.”
andyou are asking an open-ended, hypothetical question: “What if ______ happened?”
. Your question boils down to "why didn't they do this thing I thought they could maybe do?". There is no actual link between Jarvis and J.A.R.V.I.S, there is no reason why one should look like the other.