ACoC is being used, just sparingly.
It was revealed to be the power of the strongest. There is no specific drawback to it, it's simply too strong for the protagonists to use all the time.
Since its reveal, it's been used only once characters have gotten serious, and that's how it will always be moving forward. The reason is that the protagonists will simply be too strong for the vast majority of their enemies so Oda will hold this in reserve until characters get serious, otherwise, he'll kill all tension.
Does it make narrative sense? No, but it doesn't have to. It's human nature to play with your food and challenge yourself - anyone who competes in anything will know that there's levels to seriousness and how much you're trying. You can be playing w your opponent, you can be semi-serious where you're trying but not going all-out, then you can be super serious where you're actively trying to surpass your limits.
It's like olympic sprinters during warm-up vs heats vs finals. During warm-up you're going easy, during heats you're serious or else you won't qualify but you need to keep some speed in reserve, then in finals you go all-out and throw caution to the wind.
The problem is, powerscalers will watch these characters fight and assume that people are fighting like they're in the finals all the time when that's not the case lol. Not everything needs to be so logical - take Zoro vs Lucci for example, it's not like Zoro was fucking around not trying for all that time, but he wasn't super serious either. Once he got angry and got serious, the fight was over in 2 pages. He did the same thing to Apoo. Characters aren't using ACoC all the time because they don't yet feel the need to, simple as that. Once they get super serious and it's time for the finals, they'll pull out all the stops which will include ACoC.