Hi Carlos,
Yes, translators are encouraged to use Damned Lies instead of accesing Git directly, but some translators (me, for example) might use an automated script (1) to push a bunch of translations instead of doing it one by one in Damned Lies, which implies so much click-work to upload and commit a PO file into a single module.
Of course this is a very isolated case, since not all translators use this kind od tools nor need access to git. In my personal case I've also fixed wrong strings in documentation or commited patches into several modules, so I needed Git access.
About merge requests I don't know exactly how it works, but I don't consider it be neccesary for translations. It could also generate a high-traffic for maintainers and delay translators daily work.
