A lot of people don't know that stamina (not the primary stat STA) and the yellow bar aren't classic and don't mechanically function correctly.
The staff a long long time ago attempted to fix it/add it but it was so horribly game breaking/broken that they reverted the change. Never again have they talked about it or attempted to make it classic.
If implemented as per classic, it would have some impact on melee classes and spells that regen stamina like
acumen and
Jaxan's Jig o' Vigor would be more commonly used.
Swimming in circles to afk gain swimming skill? Have fun drowning when you run out of stamina.