Do you contend Israeli intelligence is the dumbest in the world?
Maxwell was dead at that point so it wasn’t as if they blew his cover. That he was a shady figure with intelligence connections was suspected by many. Foreign governments would already have known the general outlines of what Maxwell was doing, and before the internet the chances of you or I finding out how many intelligence chiefs attended his funeral were close to nil. It’s also possible that what they were trying to conceal was an assassination of Maxwell, who died under suspicious circumstances. Whole books have been written about Maxwell’s doings. If you really want to know, dig into them yourself.