Because RM is Advaita, and Advaita also teaches that
reincarnation happens when there is ignorance and vasanas. Its
similar to Buddhism, in Buddhism rebirth happens due to ignorance
and karmic tendencies or afflictions.
But what we consider as 'ignorance' is different from them.
Sir the Nirvana in Buddhism and Nirvana according to Ramana is
the same isn't it?May be same target,different routes? And soul is
part of Brahman as I understand.