Since the only real reason for carrying an official handicap is to play in competition, doesn't it make sense to play handicap eligible rounds with other people, just as you would be required to do in a tournament? Some players play worse when alone, others play better. That can be in part due to the difference in the speed of the game, or in the uneven flow when a single is playing on a course filled with mostly other groups. In either case it doesn't do a very good job of simulating the play of a four player group in the typical competition round.
Another point made previously in this thread, but maybe missed by a late participant, is that this is nothing new. Until the mid 90's, all players carrying a USGA handicap were required to return a physical scorecard, signed and attested, for every qualifying round. The new regulation is much less stringent than that, so I find all of the complaining about it to be rather amusing.
If the various handicap systems around the world end up being unified as has been rumored, then I have a feeling that the rule will become even more strict than it is right now.
But as has been noted before, it doesn't have to be a golfer.
Do the other handicap systems require the "accompanying person" be a golfer? (If so, the USGA might be expected to change that in the future, if they are to be unified.)