The author is focused on GPU texture compression for games[1] so they're not too concerned with fast compression speed. Given a game will be played on (at a minimum) tens of thousands of machines, some of which may be quite limited (e.g. handheld consoles or mobile devices), the game developers are only more than happy to trade off once-off compression times for decompression size / speed. They'd likely only perform this on a later "release build" of their game too.

The author mentions in a tweet going from minutes to seconds for compression when switching CPU for GPU[2]. From memory he has made other references to a few seconds for compression being entirely reasonable for such tasks but I can't find a direct reference.

[1]: http://www.binomial.info/

[2]: https://twitter.com/richgel999/status/1476325003662667777