Why do Orthodox Jews stay up all night reading Torah and Talmud and Kabbalah on Shavuot?

Because the morning of Kabalat HaTorah, Bnei Yisrael slept in and Moshe had to come wake us all up. This was a sin because when one is exited about something, they get on at the crack of dawn and when Bnei Yisrael did not wake up early it showed disrespect to the torah