Reason for Declining
Erik Per Sullivan turned down the Malcolm in the Middle revival because his passion and love are in academic pursuits rather than acting. Bryan Cranston explained that Sullivan stopped acting as a child and got into academia, where his true passion lies. Sullivan is currently pursuing a master's degree in Victorian literature, specifically studying Charles Dickens, at Harvard University.
Financial Sacrifice
Sullivan rejected a substantial financial incentive to return for the reboot. Jane Kaczmarek revealed that the cast and producers offered him 'buckets of money' to come back and reprise his role as Dewey, but he declined the opportunity to remain focused on his studies.
Impact on the Revival
Due to Sullivan's decision, Dewey is the only member of the original family being recast for Malcolm in the Middle: Life's Still Unfair. Actor Caleb Ellsworth-Clark has stepped into the role. Other original cast members including Frankie Muniz, Bryan Cranston, Jane Kaczmarek, Christopher Masterson, and Justin Berfield are all returning to their roles.
Cast Perspective
Jane Kaczmarek praised Sullivan's commitment to his academic path, calling him 'an incredible student' and her 'favorite American right now' for knowing exactly what he wants to do. She noted that Sullivan has realized his potential through his studies and is happy with his decision to prioritize education over entertainment. 
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