You're not constrained by obligations if you choose not to make money with your product. So yes, it can be free of charge and free of obligations. Developers have to earn money somehow, unless you want Unreal to cease to exist. This model not only makes perfect sense, the product can absolutely be free in every sense of the word.

People whining about this are being ridiculous.

Why would you say that?

I actually explicitly believe that the FSF and OSI have coopted the term "free" in order to bend it to their own definition, while in fact espousing a position that explicitly advocates for licenses that restrict user freedom in very specific ways.

They, of course, happen to restrict freedom in a way that many folks like. But it's undeniable that, from the perspective of the individual user of software, BSD-licensed open source (for example) affords greater individual freedoms than that provided by GPL-licensed software, specifically because the latter is "subject to or constrained by engagements or obligations".