Well, I think I theorized this when Klugheim was being built (or it was about energylandia), but it is simply possible that Phantasialand just puts all their extra profits into developing new stuff, instead of keeping it or dealing it around for execs. For example my home park Linnanmäki has roughly something over 1 million yearly guests (no super accurate info available) and they're able to donate over 4 million euros (roughly 4.5 million $) to charity annually, even after new improvements which means easily parks with more guests have lots of spare money (consider how much Merlin lost daily when Smiler was closed yet they survived)
This makes much sense yes. But I still wonder, because if you compare with private held parks like Europa-Park, Phantasialand still makes much bigger steps. And Europa-Park does have at least twice the visitors. Anyway, I am happy that Phantasialand is developing like that!