Dear Ashok, The OLH website is mainly concerned with this question. The information begins here. The general idea is that libraries and scholarly charities pay the OLH to produce OA journals. It's cheaper than the libraries having to buy commercial journal licenses. Plus, the research paid for by the taxpayer is freely available to the taxpayer.
How did it come to develop this model and how can it maintain (or continue to maintain) the model? The services it provides must cost something. Who pays for them?
Thanks for the guidance you are providing to Indologists.