Those questions appear in mind because you do not understand Dhamma and they reflect your desires towards the world.
“Why do I exist?” because of Paticca Samupadda
“Why isn’t everything parinirvana?” because world is Anicca not Icca
” Why am I in this Sansara” because of Paticca Samupadda and your actions
“Why haven’t I attained parinirvana in this infinte sansara?” because you didn’t meet conditions like that. The infinity of Sansara is not the infinity we can think of.
It’s very easy to answer those questions for yourself as long as you can see true nature of the world and understand basic Dhamma concepts. Those answers need to be known on an existential level, not just on a conceptual.
