Soldato
Yeah its fresh soil so you'd expect that the nutrients will decline in time and the soil is compacted underneath (turf is always compacted so you don't sink in it when you walk on it) it so they aren't going to make much headway into that it's also prone to drying out for the same reason as the two layers of soil aren't really connected.
Look up Charles Dowding, he converts grass into beds all the time. A layer of cardboard, then compost and his beds sells market garden produce. This system does work. It's simply called no-dig gardening.