The supply stands at 100 billion: more cannot be made. But the circulating supply increases, due to Ripple Inc holding on to about 60 billion XRP at this point (which are placed in escrow by the way, and only gets released in small batches). Ripple uses this 'war chest' of XRP to attract new partners, all of which that buy it are restricted it dumping it on the market as well. I do remark on that, as there is some kind of 'idea' - a poor one that is - within this community that Ripple can just nuke the market at once. Anyone that even followed the company longer than a day knows that would run counter to everything it stands for, but since most people here haven't even read more than a tweet about Ripple I will suffice by saying that much.

Ripple is actually quite decentralized nowadays. You can inform yourself here: https://ripple.com/dev-blog/decentralization-strategy-update/  And now to totally piss you off: what do you think about this:
https://i.imgur.com/UMosX0E.png ?

Is this 'not' centralized?

The big irony of some of you oldtime Bitcoiners is that you just cannot see what is unfolding in front of your very eyes, that being that BTC is actually at this point more centralized than Ripple. Good luck defending the opposite point of view.