So I’ve been looking at upgrading my PC and it looks like I can get a better “micro” pc than my current (ancient) desktop for significantly less money than a full blown gaming rig. An example of such a rig is this.
I don’t have high gaming requirements - I play mostly old games, I think the newest games I play are from 5+ years ago.
What reasons are there for not buying one of these (over a comparable “proper” desktop)?
You can do better. I’d get a miniITX form factor of your choice that supports a video card, but omit the card for now.
An amd with igpu might be decent for your needs today and slap a dgpu in later if your needs change.