Ethereum gas limit

Isn't it strange that the ethereum gas limit holds so constant for extended periods of time?

For those who don't know, eth gas limit chart looks like this:

https://etherscan.io/chart/gaslimit

But ethereum miners have the ability to raise/lower the gas limit; how is it that they all consistently agree on such a constant number?

The answer is because they can only move the gas limit within a certain range, and they are all voting to keep it as high as possible.

Is that an efficient system? If the cap is going to be artificially low (artificial in this sense meaning the voters ~always vote UP) why even vote in the first place?

Thought experiment. If the gas limit -limit (the limit of the gas limit) was 100x where it is now, what equilibrium would miners end up creating?