It's not unreasonable when you consider this in terms anticompetitiveness and related laws.
Imagine if Microsoft just came along one day and literally banned any office software, including LibreOffice etc. from running on it's OSs.
Imagine if Nissan bought up a bunch of gas chains in the US and refused to sell gas to ... to let's say ... GM cars.
Or the electric company, which had invested in some solar panel outlays, decided to ban all other 3rd party solar panels from the grid.
These things are always a little fuzzy, but they are real.
Also - the lack of user clear consent is another one ie telling users that apps 'cannot extract their data' but in reality, they are selling it to Netflix.
FB can legitimately explain a way a lot of issues lately, but this one is bad. I think it's far worse than the Cambridge Analytica scandal in which case they weren't really doing anything wrong, just late to maybe close off said APIs.