Have you submitted it as a feature request to their support? I get the feeling they just don't have enough people asking for it.
I've had the strong suspicion for a long time now that they simply aren't listening to these sorts of feature requests that don't tie into their enterprise/business focus – at least since about 2013.
We do not support markdown but have created an API that lets third party developers provide markdown support.
One really good example is www.marxi.co