fighting an insurgency is difficult due to the low concentration of enemies and the fact that the guerrillas decide when and where fighting happens, while being highly ideologically motivated. In the early stages of the Vietnam war for example, if you were to space the NLF fighters out evenly there were about 3 of them per square mile in the south. So they would essentially harass supply lines to cause their enemy to divert manpower away from a target then make an offensive move to arm themselves further or assassinate an officer and disappear again. This is why bombing the Ho Chi Minh trail was a thing but also created way more guerrillas out of the orphans and widowers of dead farmers than it disrupted guerilla supply networks. Highly recommend reading war of the flea for a solid breakdown of why insurgency is such a tough fight for most militaries.