It’s legal for a monopolist to compete on price, but when they tie rebates or price incentives to excluding the competitors product then they are engaged in behavior that is counter to a free market. I’m not sure exactly what Intel was doing, but I suspect it was analogous to MS deals that required a license payment for every PC shipped by companies they do business with regardless of whether or not Windows was installed. Note that companies that are not considered monopolies get to make the deals that a monopolist would be fined for making.