All bodhisattva will naturally become Buddha. in bodhisattva,
there is no aim, their reincarnation into beings' world are to go
through discrimination and attachment of all beings so as to
achieve full enlightenment. Some bodhisattva have stronger vow to
liberate all beings before attainment and some vow to attain
enlightenment before responding to the "sincere demand" of beings
to liberate them. As beings heavy, light karmic, affinity and
conditions varied, the timeframes on the side of beings to recover
back its buddha nature are not equal as well:)