Currently they have allocated 1 designer, 1 artist and 1 programmer.
On a typical day, an RTS like this sells let's say 50 units at $30 apiece. That's $1,500. Steam gets 30% so now you're at about $1,000 a day or $30,000 net a month.
That is enough income for 3 people to work on the game. A designer, an engineer and an artist.
Hence, we have been steadily releasing new maps and units (for free).