The short answer is that it was useful! The parameter space of things that have been tried in uncountable organisms over _billions_ of years is vast.

And proprioception is incredibly useful, even in small doses. Imagine you're a single-celled organism:

At the simplest level, some vague sensory input about your surroundings so that you can avoid the predator/find the food gives you a massive advantage over other organisms that can't. Every random mutation that improves this ability, even a tiny bit, is rewarded, as you can grow faster/die less and ultimately, reproduce more. (this is what we call "fitness" - how many of your genes get passed on).

If you get a mutation that hurts this ability, you're going to be massively penalized - eat less, grow slower, reproduce less.

In pretty short order, the organisms with higher fitness are going to take over.

Mutations occur all the time. In humans, the rate is very low - about 3 new mutations during every cell division. In many bacteria, the fidelity rate is much lower, and the reproduction rate is much higher, and so they are _constantly_ exploring new combinations of parameters. Most are neutral, many are disasterous, a few give a slight advantage.

Pile up these small advantages over millions or billions of years, and gradually, in fits and starts, very complex abilities evolve.