if you look at Mac Mini design, it didn't change much in many years (2011-2024 is practically the same)

https://preview.redd.it/always-loved-the-design-of-the-mac-m...

so maybe that's the reason they chose it. They just designed a new iteration in 2024, so maybe they don't expect much change for a while.

The guts on the inside changed several times during that timespan.