I think a good bit of that was Giles' influence. He seemed reluctant to move into the 20th Century, distrusting computers and furnishing both Buffy and Faith with weapons that, while they might have been traditional, were to say the least antiquated. A prime example is the museum piece crossbows used on the show, Compare one of them with one of the new Barrett Compound crossbows, and it's like comparing a Model T Ford with a new Mustang GT. Wesley used firearms often and quite effectively on "Angel," but aside from one rocket launcher, and that actually used only once, everything Buffy used belonged in the museum. But weaponry is a topic for another discussion, used here only as an example.
Giles distrusted and avoided anything modern as applied to his Slayer. It was quite obvious on several occasions that he even found Willow's use of the computer, regardless of how helpful it might be, somehow distasteful. Even in Season 7, he rants about how terrible it is that all of the library's contents are on computers rather than in printed volumes on shelves. If any member of the Scoobies would have even suggested the use of anything as modern as a cell phone, he would have gone into apoplexy.
