This seems to be sloppy wording, with the intent of "we only offer the bounty under these terms". Maybe my interpretation is too charitable.
I do not speak for MSFT, but last time I spoke with MSRC indeed they would be happy to receive your vulnerability report even if you did not wish to participate in any particular bug bounty program.
I do not speak for MSFT, but last time I spoke with MSRC indeed they would be happy to receive your vulnerability report even if you did not wish to participate in any particular bug bounty program.