When I was younger and more enthusiastic about some aspects of network communications, I set out to understand ASN.1 by reading the specifications. That was when ISO and ITU-T were even more stingy with access to their standards/recommendations, so it wasn't easy to get them as someone with no connection to standards bodies, and also without a few hundred CHF to spare. Reading those specs is an art in itself, but one gets a hang of it after a while. It went pretty well until this part of X.208:
The resulting type and value of an instance of use of the new value notation is determined by the value (and the type of the value) finally assigned to the distinguished local reference identified by the keyword VALUE, according to the processing of the macrodefinition for the new type notation followed by that for the new value notation.
That's where I burst out laughing and finally deeply understood why the ISO networking stack crashed and burned despite having some solid ideas.
All this is to point out that yes, DER is not bad at all, but the whole infrastructure it rests on is simply too alien to people outside of telecom space and those who have to deal with it by necessity because of its use in various security protocols.