In this thread, it was suggested that the OPL might not have sufficient/appropriate tags for physics problems, and that might be the reason that more physics problems haven't been migrated to the OPL. I'm new to WeBWorK, and don't know all the ins and outs, but as someone who is preparing to write a bunch of physics problems, this is something I could probably help with.
OPL Maintenance
Physics tags for OPL
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