He literally explained why he included that part. If you are a player with very few champions but have reached gold, it only makes sense you'd be concerned about getting a skin for a champ you don't own.
Victorious skin has been for a champion important to the meta every single year.
Morgana, Orianna, Maokai, Graves etc are or were very popular champs when they received them. Maokai was pick/ban status in top lane when he got his.
Regardless of how popular the champ getting a victorious skin is or isn't each year there are a lot of new players, or players with secondary accounts, wondering if they need to go buy the champ beforehand to be eligible for the skin. It's well known you don't to veteran players, but they're not the only part of the LoL audience.