i strongly doubt Nasu is ashamed of their eroge roots. They rereleased the R18 version of Fate, and most of the writers he hangs out with and gets to write fate are eroge writers (sakurai, higashide, meteor, urobuchi). Nasu being ashamed of it is something pushed by either people who belittle the medium or doomposters who want them to go back but do it with a pessimistic, accusatory tone.