Thats not really what they're for though that have the effect too. Most of their usefulness is that they prevent a dos attacker from filling up bitcoin node's disk space with long runs of low difficulty blocks forked off low in the chain.
This is a special case of isolating a node from the main chain and feeding it the blocks of the attacker's chain. How is this not related to security?
It's a DOS angle, nothing more. The key distinction is that bitcoin can continue to function with the same level of security with checkpoints removed. If you remove checkpoints from any PoS coin, it immediately becomes vulnerable to any number of attacks on the chain history, for example the keys from the past attack wherein I can produce invalid candidate histories by using historic private keys which are no long in use.
In theory pigs can fly. I can name a number of theoretical attack vectors on PoW coins. They don't make me lose sleep owning PoW coins.