One of the nicest things about Byte Buddy is that it allows you to write a Java agent without manually having to deal with byte code. To instrument a method, agent authors can simply write the code they want to inject in pure Java. This makes writing Java agents much more accessible and avoids complicated onboarding requirements.
After the first successful experiments, agent authors often get hit by a wall of complexity that the JVM throws at them: class loaders (OSGi, oh my!), class visibility, dependence on internal APIs, classpath scanners, and version conflicts to name a few.