That's a bit ahistorical. The "September that never ended"[0] (aka "Eternal September") was in 1993, the Canter and Siegel Usenet spam[1] was sent the following April. The DejaNews acquisition[2] wan't until 2001.

[0] https://en.wikipedia.org/wiki/Eternal_September

[1] https://en.wikipedia.org/wiki/Laurence_Canter_and_Martha_Sie...

[2] https://en.wikipedia.org/wiki/Google_Groups

Usenet spam started in 1994, before DejaNews existed.

https://en.wikipedia.org/wiki/Laurence_Canter_and_Martha_Sie...

Not sure, wiki puts that as 2001, and I remember being annoyed with spam in the 90s.

I think the rise of web-based forums is what killed off usenet as a general tool.