Question about tenacity

Why is tenacity most accessible to those who need it the least like tanks and brawlers as opposed to squishies. I'm not saying tanks and brawlers DON'T, need it but as a tank or brawler if you get charmed or something you're far less likely to die unlike adcs mids etc. However as a brawler it's more understandable because they're still squishy but they're not guaranteed dead because of one hard cc ability that's affected by tenacity. The only item in the game that doesn't provide pure defensive stats is , and it's not even real tenacity or a pick that feels good or provides useful stats on any other role besides adc. It just seems a little counter intuitive to create a stat whose purpose is to save you or get you out of a bad situation easier, is most readily accessed by characters who don't need to be saving as much. I'm just wondering what the design purpose of this stat currently is.