Outside of some stage actors and drill sergeants, there are probably few people who can project their voices well enough that a vocal warning is useful.

You're either traveling slow enough that it's not necessary (and why yell at people if you have to?), or are too far away for someone to understand and get a bearing on who isn't already looking at you.

A bell is still rude in a shared space but used correctly, a decent one can at least be effective.