Why wasn't Jiraiya burried in the Konoha Cemetery?
As JNat stated in the comments, this is a memorial for Jiraiya rather than an actual grave. Jiraiya's body was unrecoverable at the bottom of the sea, so there was no body to bury in the cemetery. 

But given Jiraiya's importance and status, why wasn't he given a proper funeral?
Well, Naruto built this memorial outside the village shortly after Pain's Assault. This is likely due to the fact that during Pain's Assault, Konoha had just been destroyed and time to hold a funeral was not a luxury they had.