Why are all the good chart generators that aren't dwarf fortress-esque always for-profit ventures?
If you'd like to build an equivalent open-source library, though, you have my vote.
I just wonder what it is about visualization that lends itself to monetization.
I would argue that among tools written for the layman, the commercial versions seem to be better than their OSS counterparts. This isn't universally true, but people without expertise are often willing to pay some money to not have to develop expertise. When it comes to visualization libraries, there are plenty of high-quality visualization tools that are highly accessible to the experienced developer, but not to the layman. Developers don't have much incentive to make them easier for the layman to use outside of financial motivation.