That's for (at least) the following reasons:
- it seems a bit odd to do the whole processing via a service - and afterwards download the output via a download link
- the current mechanism is inconvenient since the client is responsible for remembering the order of the requested export formats and match them to the several download URLs; by providing a service method the service may encapsulate this information
The service method might look as follows:
with the following query parameters
If you think this service method is desirable, please vote for this feature request.