Quote Originally Posted by shinta|hikari View Post
You need time and resources to educate others and create more tools. Maybe they are busy just producing the limited amount they have now to do that. The whole demon slayer organization isn't exactly an example of stellar management, what with letting promising disciples die in a test against a fat demon with a vendetta instead of purging said fat demon and letting disciples grow stronger with more experience.
If I remember, the purpose of that demon, or others like it (because the others obviously passed without fighting it specifically) is to set a bar.

A candidate might have the will for revenge, they might have the drive, or show aptitude in one of the styles.

But they'll still die and become fodder for the demons, or worse (the little spider heads that Zenitsu almost became for example) if they can't manage that level of threat in the field on their own.

We see the main trio working their way up the ladder of demons throughout the series. But there's lower levels slayer running all over the place killing fledgling demons like Tanjiro faced early on.