Forgotten not in the sense of lost knowledge, but more that the individual is not known proportionally to the importance of his work, or perhaps consistently when compared to his peers.

While specialists in his field know his work and his name (but not even everyone in software does), the public do not.

While your parents and friends see the dramatised exploits of Turing in films like The Imitation Game, or his face on the currency, the same is not said for Church.

Every field has it's public heroes, usually related to the stature of their work - Fleming and Jenner, Marconi, Ford, Bell. Turing.

Anyone will at least recognise these names, but not so for Church.