I'm not certain if it predates the radio compulsory licensing, but I think the compulsory licensing for recordings is at least as old, so it's not about limited radio spectrum, it was rather about preserving certain rights that people were worried copyright would unduly restrict.

Well, in the US, copyright exists "To promote the progress of science and useful arts" I can argue that being able to be able to get movies in one place is certainly useful. Or that it seems reasonable that in exchange for the unnatural monopoly of copyright, strings can be attached.

All property rights are "unnatural" (animals don't recognize property rights, only possession). In my view, copyrights are the least unnatural. We grant property rights in land with few restrictions, yet real property rights are a greater restriction on freedom than copyrights. A copyrightable work, unlike a piece of land, is the fruit of someone's labor. Land, in contrast, pre-exists the owner. And whereas land is a scarce natural resources, the universe of copyrightable works is unlimited. There is no good reason to attach more strings to copyright than to real property.