1. Tail as a measure of strength: Kurama often uses the number of tails to determine the power of a tailed beast. However, this is not the case for Gyuki and other tailed beasts. Gyuki's strength is not determined by the number of tails and may even surpass some of the other tailed beasts.
2. Gyuki's competitiveness: Gyuki is a competitive tailed beast who refuses to accept being labeled the weakest among the nine tailed beasts by Kurama. Although Gyuki acknowledges the power gap between them, this further fuels Gyuki's anger towards Kurama, leading to constant bickering.
3. Gyuki's sealing ability: The main reason for Kurama's dislike is that Gyuki possesses the ability to seal Kurama, which Kurama has no way of countering. Even though the Eight-Tails, Killer B, also possesses sealing abilities, it is not comparable to Gyuki's. This ability is essential in countering Kurama's power.
In summary, Kurama dislikes Gyuki mainly because Gyuki's sealing ability poses a significant threat to Kurama, while Kurama lacks the ability to counter it.