Such data scrapers are in a lot of cases against the terms and conditions of these sites.
There are attempts out there to use APIs. This recent post should give you all the info you need to know why it can not really work out in the long run: KiCost going quiet
(TlDr: the data providers are not really interested in giving away their data for free.)
Not only that, but from what I heard, KiCost used data from Octopart, and Octopart is bought by Altium, which is a (very expensive) competitor of KiCad.
On the ohter side of the spectrum, DigiKey is maintaining KiCad libraries with parts they sell, probably with their part numbers.
The digikey libs for kicad are a very small subset of parts.
The libs are also setup in a very bad way (not very scale able as they have only one large footprint lib with lots of unrelated footprints in it.)
This makes it unlikely in my opinion that this library will grow much further. (I guess they thought they provide a small lib to get a bit of publicity but did never intent to get all of their parts into the library.)