The reason people put it on pitch decks to investors is that investors care. Now, this can be explained by investors being stupid. But there is at least one other explanation:
VCs are trying to hit the 1 in 1000 startup that makes it big. These startups are, necessarily, aiming at a large market. The VC realizes that, if the size of the market is huge, your chances of getting a good chunk of that market is small. But so what? They'd rather fund 100s of startups that will fail, but are all trying to make it big, than fund 100s of successes that are mediocre successes (to them).
Of course, as a founder, this isn't the math you should be doing; not by a long shot. But it is what matters to investors.
The reason people put it on pitch decks to investors is that investors care. Now, this can be explained by investors being stupid. But there is at least one other explanation:
VCs are trying to hit the 1 in 1000 startup that makes it big. These startups are, necessarily, aiming at a large market. The VC realizes that, if the size of the market is huge, your chances of getting a good chunk of that market is small. But so what? They'd rather fund 100s of startups that will fail, but are all trying to make it big, than fund 100s of successes that are mediocre successes (to them).
Of course, as a founder, this isn't the math you should be doing; not by a long shot. But it is what matters to investors.