I've heard that Dracozolt is quite good in VGC, but I don't see many users using it, so what is the reason, it can't be just because it has terrible accuracy in everything.
Dracozolt is viable in VGC, and there are a lot of people using it. I don't know why you haven't seen those people.
source (note that Series 6 is called "gen8battlestadiumdoubles" in the stats for some reason)
I think a big reason is because more Pokémon are immune to Bolt Beak than they are to Fishious Rend. Every ground type would have no worries against Bolt Beak, but to be immune to Fishious Rend the Pokémon would need an ability such as Water Absorb or Storm Drain.