Keldeo is a powerful water-type attacker who eats most Special Walls alive when in rain or with a Choice Specs - can Crawdaunt get past its Physical Walls? Azumarill has superior speed, typing, and defenses. And Gyarados is still the monster that it is, with more switch-in opportunities than Crawdaunt and can set-up on a wider field, in addition to countering the top threats in the tier - and that's without having Knock-off or priority.
Crawdaunt couldn't manage to make it to OU last gen when permanent rain pushed so many Water types over the top. Its competitiveness in the current gen has only gone down now that there's no perma-rain, there are so many tougher and faster pokemon in the tier who can either absorb its hits and KO back or just KO it outright, and its only niche is a really strong STAB boosted Knock-off, and if I wanted a Knock-off user there's a really good group of pokemon in OU who can fill that role - Bisharp, Mandibuzz, and Mawile, to name a few. I know that "Just because a pokemon isn't OU doesn't mean it sucks", but Crawdaunt is just too outclassed by the environment to be worth bringing in your team.