I figured out the reason why minimal logging was not being done in my case.

All the pre-requisites mentioned in BOL to achieve minimal logging were met.

Though, a few hours later I noticed that my target table has an IDENTITY column, and I thought of removing the identity property or the identity column itself and see if it makes any difference.

And lo, minimal logging was achieved.

Not very sure of the internals behind it, but if I remove the identity column from the target table, the 150 million records insert is minimally logged.

Do you think BOL should mention this exception or add it in the list of pre-requisites for minimal logging during normal INSERT..SELECT operation?