This is not true most grants do not allow for OA money or you have to take it from other lines (salaries, equipment...) and deal with that internally. But in the end it is taken from your research fund, the university is also taking a portion of the grants as indirect costs and a part of those pay for the yearly increasing secret library contracts (they are confidential you can't even get them with a FOIA). So in the end paying OA to large publishers, you are paying them twice.