Duckweed problem

I have a duckweed problem. But not in the way you think. I genuinely cannot grow it 😭 I have it in 4 different tanks and it only grows in one, although to be fair that tank is stocked up. It never grows crazily like everyone talks about, I'm wondering if it's because most of the tanks I have it in only have snails and shrimp in it so they aren't feeding a lot?? I dont know