For me, it's just genuine interest of why there's a dearth of good and solid Tactical Role-Playing Game in the market recently.
One can only play Xcom: EU and its expansion so many times before boredom started to set.
Other indie tactical games are very light on the tactical side, very simple or very buggy with bad implementations and broken exploitable rulesets.
So, instead of constantly complaining about it, I try to make a change about it by creating my own TRPG, one that me and like-minded people would have fun playing for both the gameplay and the story itself.
Hence all my previous attempts until my recent one, Gangster Tactics.
I won't say that financial gain is not considered by me since that will be false but when I concentrate in this genre, I pretty much already understand that tactics RPG have low mainstream appeal due to people consider it time consuming and hard. The profits won't be good and I prepared for that.
Even so, I am still driven to at least create a game in the genre that I like the most.
So, in short, I like tactics RPG and therefore is creating one.