I think the reasoning behind using an RTS is likely that the company wants people to write inherently online games on their platform as part of whatever monetization strategy they have - and the other big alternatives are the MMO and MOBA genres, which would need a lot of content to be made. Having a couple of bright programmers on call - the designer is both a Starcraft celebrity and a mathematics nerd, so he likely can chip in too- would no doubt be cheaper than hiring enough artists/character designers or voice/motion capture actors to make a respectable game in some known hardcore online game genre...