Why are Mastery 6 and Mastery 7 locked behind crafting?

The idea of making players get a certain amount of S's on their main champion is a great idea but the way its implemented is really subpar. I got league solely for Gnar, not even fucking around with you here. I started the game with him, and i've mained him top lane for a long time (although lately I've been interested in other top laners like Kled) so around the time Champion Mastery was added, I was hype as fuck, Gnar was the first champ I got to M5, then the others were just secondary picks I also favored, like Sivir and Lux. So, when M6 and M7 were added, I was even more hype that I could show how good I was/ my experience with the champion I consider my top lane main, until I realized that you have to fucking buy champion shards to get m6 and m7, then I was annoyed. Why? Just why? I don't have everything in the game, I still have tons of runes I need to buy, and I still have about 43 champions left I need to get. Why force me to waste my ip I could be using on champions or runes.

I get it if people respond with "Well, its purely cosmetic, it doesn't really matter, or its here for players that have everything already." but like, M6 and M7 are the only champion masteries that require an S ranking, M1-M5 can be gained purely through playing a champion, no matter how bad you are at them, you could be a subpar riven or renekton player and get M5 with ease if you have teams that carry you through. M6 and M7 are solely dedicated to showing your experience with the champion so why paywall lock it? I don't want to waste my IP on stupid champion shards to show that I'm experienced with Gnar. Could you guys possibly find different content for people that have finished the game to get rather than a useful feature such as mastery?

PS: JESUS, ITS SO HARD TO GET AN S ON GNAR BECAUSE OF HOW POPULAR HE IS NOW HASFHAFHASFAJFKAKFA