I have also heard this so I did add some for them when my hen went broody. I think they like to feel safe when hatching the eggs, so I think mostly they need some nooks or brush to hide in.
I don't have live grass, just hay, cut branches and my coop/run is one integrated thing (4x10) (I guess...
I have had a coturnix hen go broody once last year, but mine are kept on dirt in a natural-ish environment. I hope to have it happen again this year as it's a lot easier than using a bator/light as the mama quail is doing the work for free.
I agree with le_bwah, broodiness will only happen if...