This is the point people miss. Same as wordpress vs creating your own blog. The more popular the software the larger the interest and the bigger exploit if successful.

It is less likely, though, and more likely to get fixed everywhere fast.

100,000 easy to crack implementations with obvious errors isn't really more secure than 1 super difficult, super well optimized/secured implementation, is it?

It is more difficult to crack 100,000 different interfaces because the time required to learn each one is a fixed cost. Having one central implementation makes it much easier to expliot because if an issue is discovered it can be immediately used everywhere. Don't put all your eggs in one basket.

> more likely to get fixed everywhere fast openssl bugs were around for a very long time

exactly. a very shitty unique implementation is much less likely to be hacked than a near bulletproof implementation used by millions with a single flaw.