How do you get hextech chests?

So I used to get hextech chests a reasonable amount but now I haven't got one in weeks after getting multiple S's. It is making it so that I cant get any skins and I cant level up any of my champs to level 6+, why is this happening. It is bothering me because I really want level 7 on master yi but I don't have enough champ essence to get it. Another thing is that in my opinion getting level 6+ shouldn't cost champ essence. It's just dumb in my opinion. It doesn't even do anything that actually helps you. Just let us level up our champs by getting S- or higher not champ essence. I want to know what everyone else thinks so post your opinion in the comments. Tbh I'm kinda sad that I cant level up my champs