[WhyNotHugo]

The grass proves that it's actually fertile lands, and that there's resources for keeping it growing.

Historically, using land with such properties for grass instead of crops was as sign of wealth, especially for large estates.

[AlotOfReading]

Grass doesn't prove it's fertile before modern fertilizers. Natural grasslands are often resource-poor places that most other plants can't tolerate. We sometimes replace one for the other because our main crops (wheat, maize, rice, sorghum) are all grasses, but e.g. Versailles probably would have had more forests, lakes, or a vineyard if it didn't have the gardens and lawns.