Once the terrifying swarms of wild beasts are removed from the land, the deep divide between the Egyptian king's promises and his actual behavior is fully exposed. As soon as relief arrives, his fear fades away, quickly replaced by a renewed stubbornness. He simply strengthens his resolve and hardens his heart once more [אבן עזרא].
The primary approach among commentators notes that Pharaoh repeats the exact pattern of behavior he showed during the plague of frogs. He breaks his clear promise to free the people the moment the danger passes. This is considered a massive disgrace, as a ruler is expected to keep his word [רלב״ג]. The situation is far more severe now than in earlier events. Previously, he simply refused to listen, but here, he breaks a direct, personal guarantee to let the Israelites go [קאסוטו, אלשיך].
His stubbornness at this specific moment is especially surprising. During the plague of frogs, the creatures died and their bodies remained in Egypt. In contrast, the wild beasts do not die; they simply leave. Pharaoh should logically fear that God could easily bring them back at any moment. Despite this obvious danger, he chooses to take the risk and harden his heart [ספורנו].
His defiance is also notable because of his sudden isolation. During the first three plagues, the Egyptian magicians stood by his side and supported his resistance. However, after they admitted that the previous plagues were the work of God, they abandoned him. Even though Pharaoh is now completely alone without the backing of his advisors, he still finds the inner nerve to remain stubborn [רבנו בחיי, צאינה וראינה].
Despite this outward defiance, there is an opinion that the plague does leave a partial impact. Pharaoh realizes that he is being punished for the brutal enslavement of the Israelites. Consequently, from this point forward, he actually removes the crushing physical labor from them. His critical mistake is believing that easing their working conditions will be enough to satisfy God, leading him to refuse the final demand for their complete release [העמק דבר].
Finally, his continued wickedness carries a hint about the future. The fact that he manages to harden his heart yet again reveals that his mental endurance is wearing thin. It implies that his inner strength is running out, and if another disaster strikes, he will lose the ability to resist and will finally be forced to let the people go [ביאור יש״ר].