All good platforms distinguish between things that absolutely must be up-to-date and those things that can probably wait and save resources.
Directory Items appears to update every hour. This means that it is much cheaper to show the same result to each individual user rather than have it calculated on demand each time a user tries to access it.
The source code is your friend:
And yeah, you might be able to increase that frequency with a simple plugin, but be wary of the resource and performance impact you might have.