^Bob had reached the end of its serviceable life, could no longer operate in rain and spent large amounts of time closed as they tried in vain to sort its issues.
Additionally the original new coaster planned for 2020 was postponed as Efteling's expansion plans were refused permission (a struggle that continues today) - so a new ride was needed elsewhere in the park.
Plus Max & Mortiz has a vastly higher capacity of 1800, actually has a story, theming, show elements/effects and onride music - the park and their family market its totally an upgrade.