Why do you say they didn't?

Would you say the Bushwhackers and armed bands of Kansas, Missouri, and much of the West count as guerilla tactics, or the various cavalry raids conducted behind the lines on both sides? Or even John Mosby essentially carving out an entire portion of Northern Virginia as his own personal domain through his use of mounted bands?

I would say it greatly depends on what you, OP, consider "Guerrilla tactics" to be vs what they might academically be defined as.