ED prizes immersion as core gameplay. Look at the rest of the GUI to understand: thruster capacity is shown when used, ammo is projected on the weapon (not on the corner of the screen), other suit stats that are easily measured or tracked are also shown. UI is minimal and use-oriented. The only caveat that breaks immersion is showing health as percentage, and this deemed necessary to keep clear feedback and keep it consistent with ship gameplay (also because the average shooter uses the "tint screen red to 'show' health", so it's necessary to separate EDO from that feeling).
Learning your sprint limit by feeling and practice is considered by the game a skill ("git gud"). The sound of your breathing is an indication of how close to exhaustion you are. There is also the condensation of sweat on the helmet. There is already an engineer mod to improve sprint limit, should you care so much about it.
Thinking the lack of it is a developer mistake just means you don't understand the design intention. Sure, feel free to complain that the lack of it for immersion doesn't suit you, that's fair and valid. But placing it as "FDev made a poop" is just petty ignorance. Wanting EDO to be what you want doesn't make you right, just shows you're playing the wrong game for you.
There won't be a stamina bar ever, unless someone mods it in. Or you all keep screaming loud enough until FDev gets tired and gamefy the UI putting it just to shut you, going against the game design, and hoping there won't be other requests that try to make EDO more of a twitch reflex shooter.
I like ED as a sim but I'd rather they improve the BGS. 
