When writing a compiler, it is useful to include the ability to dump the abstract syntax tree in a human readable format, for debugging purposes. This output might also be useful for other tools like IDEs and code analyzers, so I might as well provide it as a documented feature.
Given that, what format would be the most useful? It doesn't make much difference to me as long as I can eyeball it, so I might as well provide e.g. whatever other tools would find easiest to read.