There was very little until the 1990s, and if the first spam was in
1978,

You're exactly right: there was very little in the early '90s because
the Net was very little until the '90s. Obviously.

then we had about 7 years of good networking before there was any.

I'm curious as to what you mean by good networking. And what you mean
by 'there was any'. Like, any _what_? Those two idiots Canter & Siegel
were already spamming Usenet in 1994.

Yes, because in 1993, commercial public access began. There was very, very
little spam during the days when the Internet was confined to academia and
research labs. Back then, when people talked about "spam" they generally
meant announcements that were on-topic but were considered too commercial.