goosefoot, weed, fallow field
萊 centers on uncultivated, weedy growth: a fallow field overrun with plants like goosefoot. It refers to both the weed itself and the neglected land it grows on.
萊 combines the grass radical 艹 with 來, which likely contributes the sound. The character originally referred to a type of weed or overgrown land.
The grass top 艹 over 來 (which resembles a plant with drooping leaves) suggests a weedy plant taking over a fallow field. Picture goosefoot spreading across neglected farmland.
For ライ, imagine a field overrun with weeds that look like rye grass: rye -> ライ, and the fallow field is full of it.