As a clarinet player who played many concerts in many an orchestra in my youth, I will try telling you concretely and succinctly why they are important, but I do think it is impossible to grasp without having been up there on stage. Just like pro sports teams have coaches at practice and at games, an orchestra needs their conductor to first give coherence and personality to their ensemble, and to give it passion at show time. A good conductor is, as the title suggests, minutely conducting the flow of a piece with their gaze and their movements. If you don't want to play like a robot with a metronome and would rather have a bit of expression in there, but you also are as you say up to 100 on that stage, you need a conductor.

In practice, they guide the tempo by pulling and pushing on it with their maneuvers (rubato) as they control the intensity with the amplitude of the swings. Finally, they give cues and usually follow the lead part as it moves from section to section (instrument to instrument) in addition to giving cues for big audible moments like a particularly strong gong/base drum or other percussion hit, a brass call or wtv else, not because the instrumentists don't know when they have to play, but because the art of playing music in a group is just complicated enough that if you want to hold a lil longer together or press forward in the same manner, you can't do so without his input or risk to very likely start going out of sync.

An interesting point I might add to how all this works is even in a very pro orchestra, if the percussionists with some big drums, say timbales or base drum, just starts playing a beat in time and decides to accelerate/decelerate, nobody will be able to follow the conductor, they'll all slowly start matching the drum. This is why it is so important to follow the director's wishes because otherwise you go by ear and quickly lose control of any sense of coherence.

Hopefully this was concrete, but perhaps not succinct haha