Lock-in has a very negative connotation. To me it's more about protecting their intellectual property.
I guess my question is protecting it from whom? The WHS is owned by the organizations with
de facto monopolies in their respective countries, we're all members. It's also very odd to me considering game rules are not patentable or copyrightable. I seems entirely superfluous, especially since they control all the data behind the adjustments, which is why it seems like something an MBA came up with. The only reason why I see it as possibly making good sense is that in the last USGA financials that list GHIN revenues and expenses, the USGA lost a significant amount of money on the GHIN system (however GHIN revenues and expenses are no longer directly listed).
I think you misunderstand the PCC. There is no PCC database. Every day the GHIN system calculates a differential for every player who posted that day to update their handicap. Peripherally it calculates the standard deviation of the difference between the posted score and the expected score for every player that posted and figures out if it needs to adjust those players' differentials because it was a much harder or easier day than expected. I suppose if you wanted to go crazy you could ask GHIN to send out a notice to all third party handicappers the PCC for every course so that the third party could incorporate it into their algorithm. But, I can't see any reason why the USGA or any other association would want to do that.
I don't know how the data is stored, but I can't imagine they wouldn't store the PCC adjustments (even if the adjustment were a function and not just a number), especially for folks that forget to post day of (after they get a stern finger wagging). You could store the PCC adjustment directly with the player, but a dramatically more compact way to store the data would be an object with dates, courses, and their PCC adjustment. This gets into the weeds about database optimization, but I certainly hope they aren't attaching PCC adjustments to individual rounds in a database, without any way to double check whether an adjustment was made on a specific date. Assuming they do store this data, it would be fairly trivial and cost almost nothing to allow 3rd parties to query this database table, assuming reasonable behavior, and rate limiting.
The rest of the comments I can't really argue with. I fully agree it's not a big deal, and we just have a small difference of opinion.