It is quite possible to arrive at the belief that no-one else exists or is likely to exist whilst simultaneously acknowledging that the illusion of other people existing is so powerful and ingrained that to separate oneself from it is - if not impossible - impractical and/or unnecessary.
It's also possible, perhaps, for a person to be comforted by the notion that they are the only extant being. It might offer them a certain freedom of thought and behaviour and an insulation from the cruelty of others. But the solipsist also stands to lose a sense of consequence; a sense of the impact of their behaviour upon others. If solipsism is true, this might not matter a great deal (at least initially), but if the solipsist is wrong, it may come to matter a whole lot.
Whether it is true or false, our experience to date tells us that more often than not, when we lack connection and empathy, we invite a range of negative consequences, such as isolation (perceived or real), misunderstanding, confusion... even punishment. Solipsism being real doesn't necessarily free the solipsist from these consequences. The miseries of the illusory world - where other people exist and impact us - are almost certain to accompany the solipsist and perhaps even become augmented by the personality shifts that are likely to accompany any embrace of a solipsistic worldview.
The solipsist also stands to lose a sense of connection enabled by the belief that other people are in fact real and care about them, and are impacted (positively and negatively) by the solipsist's actions, for we tend to derive much of the meaning we find in life directly or indirectly from our relationship to others; from approval, acceptance, love, admiration, companionship and so on.
Even if, upon accepting solipsism, a person feels an initial, refreshing liberty, it is likely that - if they are somehow able to maintain a continual belief that no-one else exists - they would find this form of happiness only temporary; that the notion they are the only mind in existence would gradually (or rapidly) become an existential burden. A sense of meaning might become very difficult to maintain. To repeat a quote that has been made here before:
The self is too small for perpetual enthusiasm (Huston Smith, if Google is to be believed).
Even a malicious or power-hungry person might become depressed at the notion of a solipsistic world, for there is no-one upon whom to exert one's will or power.
If the world seems too great a burden, solipsism might become appealing less because it is convincing, but because it suits a person's need to withdraw and to escape the anxiety of a life that must be lived with others. This would be a case in which a person allows their desires to dictate their philosophy, as opposed to using philosophy to dictate their desires (and beliefs). As already touched upon, solipsism might not actually offer as much as it initially seems to, for when others cause us pain, we often mistake our desire to be free from suffering as a desire to be free from others who are causing us that suffering, when in fact we are deeply programmed to rely upon them.
Is a solipsistic life doomed to self-gratification and narcissism? There's a case to be made that life is ordinarily lived - at root - in such a state; that even our attempts to serve others are fundamentally an attempt to serve ourselves. But if solipsism is real, life could be lived clinging to the illusion of other minds and maintaining a generous spirit whilst shunning focus on the self. Alternatively, every potential action might be evaluated from the perspective only of the self. In both circumstances, there seems something to be lost as well as something to be gained.