Burleson is a special case for several reasons.
First, he was drafted in 2020 and missed out on a whole summer of development. Then in 2022, he was promoted from high A to AA to AAA in his first professional season. In 2022, he was allowed to settle in at AAA and slashed a strong .331/.372/.532/.905 in 109 games. He smashed 20 home runs and drove in 87. So the Cardinals know he can hit and hit with some power.
Secondly, the Cards have had guys also with strong AAA numbers, like Arozarena and Garcia, go on to highly productive major league careers. Mo has taken heat over that and it has probably increased his patience quotient. He might not want to be criticized for another mistake in talent assessment.