Fedex will continue to charge as much as they can to boost their profits. This move will increase their profits, making $1.50 on each of 100 million deliveries instead of $1, boosting profits from $100m to $150m

However if they were to undercut UPS and others they might be able snap up UPS business, dropping the profit to $1, but on 200 million deliveries, and thus they'll make $200m instead, you the customer will have a cheaper delivery, and everybody wins