"When Joseph Caro chose Rambam as one of three poskim whose opinions he would collate in the Shulhan Arukh, the other two being Isaac Alfasi (the Rif) and Asher ben Jehiel (the Rosh), it was implicit that Rambam could be overruled by the other two." (source)

"I don't think that his opinion should not be taken seriously, but I don't know why in many communities I have been in, the rambam's conclusion is considered final above other prominent poskim when a controversial topic comes up. What is it about him that caused his ruling to be differed to to the extant that it is?" (source)