You are 100% right: netflix not being open is less than ideal, both from a freedom standpoint and for the privacy implications of it.
However, my 70+yo relative does not care about FOSS or even about their own privacy for that matter… since I, however, do care about their privacy, I’d like to pragmatically find something that may be better than a chromecast privacy-wise, while not being so much worse (or radically different) from it that they’ll ask me to “put the old thingy back - I can’t use this nerdy shit” :)