Yeah, at one point Youtube in their wisdom decided that toys are for kids, so anything to do with them got forcefully marked as “for kids”. I remember many LEGO and RC channels have issues with it. And having your video or channel marked as “for kids” disables 90% of Youtube features - comments, likes, notifications, saving videos to playlists or watch later, end cards etc.
But eh, in the end it is FTC and COPPA telling them what they have to do.

But even then, Youtube basically has only two age ratings - either the content is suitable for everyone (but you do have to mark if it is specifically aimed at kids under 13), or it’s age-restricted to adults only. Imagine if movies only had the options of “G” or “NC-17”.