Are you highly educated?

My father has only a certificate and no degree or anything like that.

It took him 20 years to get citizenship. We came 3 years after he come here and we all became citizens together.

My friends whose parents were doctors or had masters degree would get their GC and citizenships in like 5 years.

Of course high education and value to the labour market make you a good immigrant, and the lack thereof a "bad" one with less value. Is this something that surprises you?

You're conflating things. GC is different (albeit necessary) from naturalization. I clearly said my citizenship took 6 months. My GC took 6 or 8 years and I got it through my wife.

For those 6 to 8 years I had a student visa then an H1B. Despite having a PhD in the top US program in my field from a top five school.

My wife got her GC through the lottery before she finished university (ie w/ a HS diploma) with 0 years living in the US