It's incredibly irritating. It always just feels like content torn out of the game and then staggered for no reason except having something new to post on social media. Witcher 3 and Splatoon also did this type of thing, if I recall correctly.
Pretty standard practise these days. I think it's a way of extending the marketing cycle post-release since games are instantly buried in a week -- two if they're among the most hyped releases of the year. It's a problem I feel marketing teams are trying to solve and this is their solution to keep eyes on their games for as long as possible.
It's annoying when we're charged, but I don't really care if the stuff is free, to be honest. In this case, I'll grab the free stuff but I'm not paying for the nostalgia cash grab (well, maybe there are licensing fees?) stuff like BGMs from past games.