Comment by eterm

It's the other way around, and there's no obligation to even carry transactions when mining, although it's incentivised through fees.

Your mining rate is simply your hash rate vs the hash difficulty.

Conceptually, it's analoglous to rolling random numbers in (0,1) until you get to a number smaller than 1/X, where X is large.

How long it takes you to do that, isn't dependent on how many other people are also trying to do that, if you get 1 hit per hour, then lots of other people getting hits doesn't actually stop you getting your 1 hit per hour.

Now, that's not quite the whole truth, as there's a small amount of time needed for propagation of the previous chain, but with an average hit globally of ~10 minutes, that's not actually a big factor.

What could happen to incentivise people is increased fees if blocks get less common due to dropped miners, there'd be more competition to get into blocks if they start filling up.

That combined with the fixed costs such as depreciation as othes mentioned, keeps the risk of this form of failure to a minimum.