That # is really misleading - Apple's $$ is mainly from hardware sales (which includes lots of iPhones, watches, etc), they still only have a small portion of the computer market.
7.1% as of 2018Q2 per https://www.macrumors.com/2018/07/12/mac-shipments-up-in-q2-2018/
To create a Mac version BandLab will have to start from scratch. While they could create a multiple platform version in doing so, the time frame would span several years and cost 100 of thousands of dollars, if not significantly more. Considering the current exorbitant selling price and high volume of Cakewalk sales I sure they're dying to allocate the manpower & funds to jump into a market that may take them years to significantly crack.
While I too would really like a Mac version of Cakewalk I don't see it happening any time soon.