This ～ほど is basically "to the point where ～" or "to such an extent ～" (see examples here). It modifies the following clause, so the sentence cannot be split there. When it's combined with a negation, it's used in two ways:
- Partial negation (not ～, but not to the point ～); usually being contrasted with は:
It's not funny enough to surprise me.
- Emphasizes the negation itself; usually used without は:
It's surprisingly boring.
Usually, you can tell the intended meaning by seeing if there is は, but there can be a few exceptions, so you need to see the context. In your case, ほど is clearly used in the latter way (emphasizes the negation).
The original sentence can be divided into three parts:
PC users in those days were called マイコン族.
PCs were so uncommon that it (= the term マイコン族) even had a negative connotation, similarly to the later term otaku.
PC games were also unpopular.