Those are not KK254, but xx 2510 produced by various manufacturers (sometimes with different number).
Weeeellll, I wouldn't be so sure.
The Chinese manufacturers can't even agree on what
pitch a "2510" connector is (2.50 or 2.54), never mind all the other details. Who knows who first coined the "2510" name for these connectors. Heck, who knows which of the big Western connector manufacturers actually invented the original of these style of connectors. Was it Molex KK? AMP CST? Which was the clone of which? And which Western clone were the Chinese clones based on? (Based on the contacts, which are very different, I suspect KK was the original the Chinese clones are based on. But I can't be sure.)
Regardless, the situation on the PC fan connector is clear: the standard is maintained by Intel (attached). The header drawing, including the title block formatting, closely matches that of the (now obsolete) AMP part. So whether CST-100 is a clone of KK254, or KK254 is a clone of CST-100, it's extremely likely that it was TE/AMP that drew the header drawing reproduced in the Intel spec. However, given that other Intel standards from the same era generally specify "Molex XXXXX-YYYY or equivalent", and that the design of the Intel spec crimp housing more closely resembles Molex KK than AMP CST-100, my hunch is that Molex actually designed the thing.
The Molex part numbers are expressly named as KK254 series.
The Wieson part number starts with 2510.
The AMP part is listed as an AMPMODU series, though it very clearly has no relation to the rest of the AMPMODU series, much more closely resembling CST-100/MTA-100 headers.
Foxconn's part number seems unrelated.
Is it possible that Foxconn or Wieson, the other two manufacturers listed, designed the modified connector? Perhaps.
Or maybe it was really Intel itself, making something based on a mix of Molex and AMP's designs.
Of the 4 header part numbers listed in the Intel spec, two are still available: Molex and Foxconn. Of the two crimp housings, only Molex is still made. But without doubt they've been unofficially cloned gazillions of times.
They look similar but usually do not mate well in combination of male 2510 and female KK254, the other way around they mate fine.