The phrasal verb dumb down is popular. From en.wiktionary, it means “To convey some subject matter in simple terms, avoiding technical or academic language, especially in a way that is considered condescending. [eg] The public won't understand this concept. We need to dumb down our explanation of it.”
Also consider oversimplify. From en.wiktionary, it means “To explain or present something in a way that excludes important information for the sake of brevity, or of making the explanation or presentation easy to understand.”
Washed out, in its sense “Of clothes. When they lose some of their original colour from being washed so often” may also apply.
From pablum, one might at a stretch derive the verb pablumize. From en.wiktionary, pablum means “Anything overly bland or simplistic, especially speech or writing”.
• bowdlerize, “To remove or alter those parts of a text considered offensive, vulgar, or otherwise unseemly. [eg] The bowdlerized version of the novel, while free of vulgarity, was also free of flavor.” ‒ wik.
• expurgate, “To edit out rude, incorrect, offensive, useless, or otherwise undesirable information from a book, CD or other publication; to cleanse; to purge. [eg] The publisher decided to expurgate the love scene from the book, to make it more child-friendly.” ‒ wik.