The Ropes Mod v. 1.15.2-1.2.0 prevents Simple Farming v. 1.15.2-1.2.7 from dropping seeds when breaking grass. When I disabled the Ropes Mod, the Simple Farming seeds dropped as expected.

You only have to add a name to your loot pool injection, than it should be fixed. ;) Had the same issue with my mod: cech12/CeramicShears@18e8317