I think this change probably has more to do with corporate firewalls than anything else. A lot of corporate internet access isn't set up to MITM the requests (a lot of places are setup for this, but a lot aren't). If they places all their services under google.com as suffixes, places that don't MITM won't have any way of stopping it as all they can see is the request to google.com.
Given the history of Google's stance towards privacy and tracking, I think it's naïve to assume technical reasons.
It may have been ok to fall for that argument for 10 years, but after AMP, manifestv3, android's location log disaster, the recording of wifi names and countless lawsuits across the globe, it seems that the resource of good faith assumptions has been depleted. Some may even say that trusting google (the corporation) to act on technical or altruistic reasons is delusional.
I'm as skeptical as anyone about Google's privacy record but I'm not so convinced that this really helps google invade our privacy more than it already does.
I haven't forgotten because my YouTube account to this day has remnants of that move. The same with my Google Contacts, it is an absolute mess of G+ and Orkut stuff that got shoved in there at some point and Google never cared to clean their absolute mess.
