Oils have been used a lot longer than soaps. They provide moisturizing and skin protection benefits which soaps may or may not sufficiently provide for your skin type (don't know how many times this needs to be repeated). I use DIY oils ,I've never had a problem with razors clogging, or with lathering for that matter.But what does it do that a decent lather doesn't offer? You will have to be careful in the mix as some oils will clog the razor or make the lather sub par and break down.
Is it a product designed for the sake of marketing and sales?
Yes, I've tried a few pre-shave products and found that they made no discernible difference, other than having to wash the greasiness off your hand(s) before picking up the razor, leaving an oily film on the water and a scum line in the washbasin.I sometimes apply some Noxzema cleansing cream before lathering as that improves slickness. It's the only thing that has made any difference whatsoever, everything else in terms of oils or creams has been pretty pointless.