You might be a good steward but with high prices due to the education costs you take on teaching the API to others. Someone can piggy back on your work, charge a lower price and never do their own further design work.
You can compete without copying the API, just design your own or use an open source one. Yes it would be hard for people to switch libraries when they have existing code but it is possible to rewrite the client software.
It is allowed by many copyright holders. Virtually all open source software and a number of other commercial platforms particularly when the API has been designed or released by or to an industry consortium.
I see it as a perfectly valid reason not to choose a platform with a closed API and while I feel sorry for those that are locked to one theynreallynshould have considered it at the start. I still don't see it as an essential issued.
I've enjoyed this conversation but I suspect no one is watching apart from us so while I wanted to answer your questions so as not to be rude and ignore them I plan not to post again on this thread.