Dunno why that's the case. My Marsilea has outgrown both the hairgrass and glosso hands down. I received a palm size amount of it from lbsfarms
who was growing it in a low light tank. It really took off in my high light (10G w/72W) tank. It used to be 2" tall, but in high light, it grows shorter and makes a great foreground plant. I dose the tank pretty heavily w/micros (1ml of CSM/day) and that might be the case. I just moved it into the 90G and we'll see how it does in there.
I've been growing it in 76-78F, high CO2 (43 ppm) with high amounts of light and ferts. I'll be raising the temperature in the tank soon, so we'll see how it does in the 80s.