Or HaChaim on Deuteronomy 2:30/אור החיים על דברים ב׳:ל׳

1 ולא אבה פיחון…העבירנו בו, "and Sichon did not want us to traverse it, etc." Whenever the expression לא אבה is used it describes a refusal without an adequate reason being offered. Although Sichon had no reason to fear that the Israelites would infringe on any of his rights and he was convinced that the Israelites were physically unable to cause him any harm, he still refused to let them pass. This is why the Torah had to provide the reason, i.e. כי הקשה ה׳ את רוחו, "G'd helped his spirit to be obstinate."