I don't accept the premise ' people are more likely to have had a middle name than not.' Middle names are very much a recent concept in English speaking countries. (it's always a big red flag for me signalling a high probability of error when I see them prior to the end of the 18th C.)
In continental Europe more than one given name occurred earlier but was/ is recorded as all one name. Legally this is also the case in the UK. It's only a a modern, social convention that calls it a middle name. https://deedpolloffice.com/change-name/law/first-name
(I've changed my thinking about 'middle names'. I'm British but now think we should perhaps follow some of our neigbouring countries on wikitree and write all the given names in the first name box but it's not an important issue for me to spend time arguing for)
As for the preferred name box, it is probably less often used on older profiles since, as you say, we often can't know what was used. It can be important more for more recent profiles and for profiles of well documented individuals.
My father in law's given name was Robert Andrew, his preferred name under which he was ordained, which both his family and parishioners used was Andrew. The UKs present Prime Minister uses his second name in his public life.
Elsewhere, in the world the order of names can be very different. We don't cater at all well for that on wikitree.