The computer you linked is very different than the Mac Mini. The Kingdel is a knockoff NUC, basically laptop components. Notice how it maxes out at 16 GB of RAM

The computer you linked is very different than the Mac Mini. The Kingdel is a knockoff NUC, basically laptop components. Notice how it maxes out at 16 GB of RAM, no Thunderbolt, and its fastest chip is still a 25TDP U-series which is probably slower in practice than what the Mac Mini starts with (looks like a 65 watt i3 8100). The Mac Mini is indeed expensive for its specs, but it's also extremely small for those specs: desktop components in a sub-mini-ITX form factor. If you wanted to compare it to similar PCs, you're looking at the custom offerings from Zotac, etc. which also command a high premium.