Spence has the 3 belts (WBC, IBF, and WBA recently from defeating Ugas) so he has done more cleaning in this division than Crawford did because he only got the WBO belt since 2018.
That is because Terence Crawford never had a chance to compete with big names under Top Rank promotions which he always requested. Also, the fact that Spence is dodging Crawford because the latter thinks it's not worth his time. Spence on the other hand always got his preferred fight and make sure he will win all his title fights and that's what he is today claiming 3 Championship belts under WBC, IBF, and WBA as you have mentioned.
In Terence Crawford's fight history, the expected fight against Spence will be the biggest fight in his career. If he was able to unify all the Welterweight titles beating Spence if ever, Crawford will now begin to move up weight to extend some good credentials on his career. He has lots of targets if successfully defeated Spence in the process.
That's also why he decides to leave and didn't re-sign under the roof of the Top Rank Promotions after he fought and won against Shawn Porter. Bob Arum was just milking him too much without understanding his boxers as they too have boxers in my mind to help them in climbing the ladder. Now that he's a free agent, he can decide anything and will earn more without giving some cut to his promoters.
Are there any updates about this fight? Hopefully, they can announce it before the end of June.