Because an egotist is infatuated and obedient to his imperious-self...
Because an egotist is infatuated and obedient to his imperious-self, he does not have any other aim except satisfying the demands of his passions in the best possible manner; in order to meet this animalistic objective is not ashamed of performing the most shameful deeds and consider them as justified and permissible.
He wants to accomplish his animalistic goals, and in order to achieve them does not refrain from indulgence in lying, accusing, oppressing, and breech of commitments, deception, treachery, and any other acts of transgression.
Therefore, egotism is the mother of all evils which makes all acts of abjectness justified and permissible, or in other worlds, it can be said that all acts of transgressions in reality are the by-products of egotism which are manifested in different manners at different occasions-. For example, oppression and trampling over the rights of others could not be anything other than self-centeredness.
Likewise, lying, backbiting, ill-speaking, fault-finding, jealousy, and revenge all are the vices of egotism which have been manifested in these manners. It is because of this reason that self-centeredness is called as the root of all transgressions. Self-centeredness consists of various degrees and stages the highest of them leads to the state of self-adoration a self-worshipping.
Is worship means any thing else except that a worshipper in front of his object of worship humbles and bows down, and should be submissive to his commands absolutely without raising least objection? Similar is the case with an egotist person because he regards his self as an object of worship and humbles and prostrates in front of him by obeying his commands without any question. Therefore, an egotistic cannot be considered as a Monotheist.