Well, this became a lot of text. I just tried to explain my point of view (not facts) as comprehensible as possible. Here's the short version:
A company has to pay for many things.
If we had a teen coding prodigy that lived at his parent's house with powerful hard- and software and a budget of 700$, then that would be a completely different thing, so I can see where your point of view comes from.
But the 'company' part is one example for why that would not be much, since a company doesn't just have money lying around, they earn it themselves. Xform produces videogames, therefore they earn money by selling games.
If you now consider at least payment for the people that work at xform, rent for an office (I assume they don't work at home) and possible maintenance or upgrade costs for PCs and workplace those 700$ unfortunately are far from lasting you even one month of work. Plus there is always some costs that you cannot expect in advance. Payments like those are not a one-time purchase, but rather a monthly investment to keep your business from bankruptcy. For a buisness, espacially a small one, the term "enough money" doesn't really exist.
I assume that BR3 and 4 were only able to be free in the first place because of advertisement revenue by the websites thatpublished the games. Seriously, 5$ is not exactly much and personally I don't have trouble justifying the price.
Also the re-releases (not reMAKES, that is a huge difference (exept BR5, which is a remake)) were a 'side project' for the fans that were asking, and it would surprise me if xform hadn't started already on collecting ideas and started designing their next main release title, so don't really worry about that.