On the contrary, I think it's a pretty big investment. For the writers and illustrators at least.
Because switching from HH to GH requested minimal investment in writers: main character still had a dick and wanted to put it in. And moderate investment for illustrators: of course they had to redraw all bodies, but basically, main character still had his penis in someone else's hole. To put it simply, he merely had to draw the dick entering ass instead of vagina.
Now, the difficulty is higher for a female main character. Her lack of penis would first need some adjustment to the story here and there. But most importantly, all the sex scenes would need to be redesigned, not just redrawn. Because the sexual positions would have to be entirely different. So there would be a huge "sketching" work to do before even considering starting the redrawing.
So, of course, we're not talking about remaking a game entirely. Game mechanics and design could be kept, as well as the background. But whereas Gay Harem could re-use the same body positions, it's not the case for a Lesbian Heroes, and it would therefore involve higher production costs for kinkoid.
Also, although I too would like to have a Lesbian Heroes game, I think the players willing to actually put money in such a game might not be numerous enough to make said game a profitable one for Kinkoid.
In fact, it might turn out to be a better business move for Kinkoid to make a "Reverse Harem Heroes" (1 girl as a main character collecting guys for her personnal harem) rather than a Lesbian Heroes. I KNOW some women would actually pay for that ^^