The reason they do the 2 connects thing is because of money. When you buy more connects after you run out, the number you get is odd, so you once you burn those down you'll end up with one connect. You can't use that for anything, so basically it's a way to make you pay for one extra connect. It's not much, but if enough people do it they make a nice little chunk of change.
The idea is that eventually some jobs will cost more connects to apply to, and some jobs will cost less (only 1 connect). This is a recognition that not all jobs should be perceived of equal value.
So the basic infrastructure for that was put into place, although the complete realization of this concept is not yet in place.
I don't think the main reason is "about money" because Upwork would really prefer that zero contractors purchase connects. The ability to purchase additional connects is a sort of release valve to stave of complaints about not having enough complaints... It gives people an option to have more connects. But Upwork actually makes more money from the people who do NOT use connects, but who simply have regular, steadily-paying jobs with long-term clients.
If Upwork was forced to choose between contractors who use up 60 connects every month and then get a premium membership to obtain some more, versus contractors who use only a handful of connects every month because they're working steadily... Obviously Upwork would choose the latter. Because the contractors who are working steadily bring in more money for Upwork.