paully,
Maybe because the fee isn't always the same at some airlines so it's hard to put it in the upfront cost? EZY add the one-off fee for each booking, so until you get to the cart to 'Checkout', they can't really add it in. No point in adding it to the listed price because if you add a few other flights - that price becomes inaccurate.
FR charge differently based on how you pay, so that's (again) not easy to put in to a list price because they can't assume how you're going to pay. I disagree with these stupid charges, but I tend to avoid Loco's all the time.