The end game is to take full control. If Google implements Widevine on YT, and especially Widevine L1, that'll be their Hiroshima bomb for both third-party front-ends and downloaders, and even non-Android, ChromeOS, Apple, or Windows platforms as far as OS goes and non-Chrome or Edge browsers.
Like, say Google implemented Widevine L1 on YT streams at some point in the future, it would be entirely feasible that you'd be looking at Netflix-style lockdowns to Edge on Win11, or even Chrome on Win11 for that matter, with both SecureBoot and TPM2 in place, if you wanted to watch YT on PC in the future, else you'd be limited to Rokus to watch it.