I would correct your statement from "lot of jams have turned into competitions with no prices, just a recognition that has no purpose nor use" as more like "lots of jams have turned into competitions with, as main goal, quantify the quality of the work and the skills of the developers involved". Nothings speaks more when job hunting in the field of the video game industry than a portfolio filled with contest-winning works as it shows dedication, skills and the ability to work and reaching a goal under a tight deadline.

In fact, there are head-hunters out there that are following any serious Jams for medium and big developing studios. Depending on cases related to the jam, it's not that rare for devs that display high rated skills to get contacted by those people. (It does requires that a dev jam developers have properly setup his profile and contact info, obviously.) In those cases, it's not much of a case of "who wins", but more about who seems to be exactly what a certain studio is looking for.

Another approach of the jams is that it's actually one good way of promoting an early PR for a new project. Obviously in this case, a 10-days devs jams isn't really enough to make a long-term oriented project, but any 2+ months jams with any form of professional and well published coverage can do wonders at bringing a crowd for the launch of the actual full game. When you win a dev jam with a project that has potential for an actual commercial release if worked on further, it's one of those choices you got to serious think about.

Obviously, in the end it's all about having fun anyway, right? And some people have more fun at competing and winning than doing the actual tasks to compete, hence why eSports have become a lucrative thing. The same exist within the devs community where winning a dev jam is just another way of feeling the adrenaline rush of a victor.