The problem with ASN.1 is that it is big and complicated, and you only need a fraction of it for cryptography, and it isn't really used for anything outside of pki anymore.

It wouldn't be as bad if asn.1 had cought on more as a general purpose serialization format and there were ubiquitous decent libraries for dealing with it. But that didn't happen. Probably partly because there are so many different representations of asn.1.

A bespoke serialization specifically for certificates might actually have aged better, if it was well designed.