That's not actually required for free software (as in freedom), but once you buy you need to get the source as well, and should be able to do with it whatever you want.
E.g. the GPL mandates not "you will make the source freely available", it mandates "you will make the source available to everyone who receives the software".
Furthermore, the Document Foundation will still be offering free downloads of LO for macOS, they just add another way of getting it that does cost money.