UEFA adopts that position because FIFA law states that such decisions are made "in the opinion of the referee." If they decide to turn yellow cards into red cards, they would undermine the judgement of the match referee. UEFA and other bodies do not contradict the referee's decision in such cases. Removing a red card is a bit different, since it means that the player can play in the following game in the competition. However, this preserves the authority of the match officials.