Why would an intelligent and engaged reader object to seeing lengthy glossaries and appendices in the back of a novel?
It’s a sign that the author is taking themself too seriously.
It’s a sign that the author is really in dire need of a good editor.
It’s a sign that the author is falling prey to unnecessary complexity.
It’s a sign that the author is too lazy to introduce these terms organically into the body of the story.
It’s a sign that either the author, the editor, or the publisher don’t trust the reader’s intelligence enough to remember the important terms in the story.
None of the above.