<p>Does anyone know how the developers of Marlin decided to name it that?</p>

Yes, it probably is totally off-topic, but fun too, so I'll try to get an answer in, before the question gets closed.
The best place to ask would be the
Firmware - Marlin forum
, on RepRap.org.
The question is there now,
Why was it named Marlin?
and I'll update this answer, if/when I get a response...