As for why must you continue being human, that's kind of easy to answer. Because you were born as one, and have the experiences of one. The entire foundation for the mind of any human is their biological and psychological condition which has limitations, desires, etc. And the evolution doesn't change that, all it does is remove some limitations. So a human mind shaped by human desires and wants is now far freer than it is meant to be, cannot get rid of those remaining human features without losing all identity, and can fulfil most remaining wants easily.
That situation will almost inevitably lead to a collapse of one's own identity, deep nihilism, and ultimately, a sad and lonely existence trying to grasp on whatever remains of their humanity, because everything else can't fulfil the yawning void of meaning that humans are meant to fill.