Actually, it makes perfect sense, thank you. The vows made at a Catholic marriage ceremony are completely Catholic in nature, in that they contain the Catholic understanding of sacramental marriage. They are vows that embody Our Lord’s teaching on marriage, and which Church herself has engendered. Said vows are are made in the presence of the Church’s minister. Even in the exceptional case where a dispensation from canonical form has been given, it presupposes that a priest or deacon has met with the couple and all of the other premarital preparations have made to ensure a Catholic understanding of sacramental marriage has been proffered.
The ontological reality is that Catholic vows are unique. Simply saying the words somewhere else, without any reference or connection to their Catholic basis, cannot, by definition, be considered a “renewal” because it is apart from a Catholic context. It would be like Anglican and other churches who claim to be ordaining priests. We know that they are not ordaining priests, because their orders are invalid and lacking in Catholic content, no matter how many men (and women) in mitres might be laying hands on someone. They lack an authentically Catholic understanding of the sacraments, even though they may share a good portion of those beliefs. Same with marriage vows–absent the involvement of the Catholic Church, one cannot renew something that is ontologically Catholic.