Daniel Bernstein, Daniel Bleichenbacher, Dan Boneh and Thomas Pornin are professional cryptographers and world-renowned experts. Even I would feel comfortable writing crypto if Bleichenbacher was watching behind my back.
Frank "wrote" libsodium, but libsodium is effectively a port of NaCl. Frank had Daniel Bernstein watching behind his back.
Eric Young wrote OpenSSL. Look how that turned out! Has there been a class of cryptographic vulnerability that OpenSSL hasn't had?
And yet consider: for all the effort that people like Bernstein and Boneh put into writing strong, safe crypto, the entire world has blundered into vulnerability after vulnerability because the amateurish crypto in OpenSSL is the one every else ended up using.
It's as if you set out to prove my point.
Finally: you obviously know that "writing your own crypto" isn't the only way to become good at it. In fact, it's a terrible way to get good at it. The right way to get good at crypto is to learn how to break it. But that takes effort, and you can have a blog post crowing about your new crypto library just a few weeks after deciding to write one.