So far, no-one has mentioned what I think is the most common reason for girls/women not using/providing condoms, etc: If you are "prepared" (especially if it's only a first or second date), then it looks like you were "expecting" to have sex, which is a big no-no... Even today, it's not unusual for women to be concerned about looking "easy" or "slutty"; you may be afraid it will look like you're "too eager" if you have a condom easily to hand (so to speak).

It also interferes with the fantasy (for both parties) of a "good girl" intending to "be a lady" but being overwhelmed by the irresistible charms of her young man -- powerful stuff (especially when you're young)!

Note: I'm not saying I consider this a good thing -- just trying to respond to the OP's query, "Why?"