Date- 13 April 2321
Time- 10:21
Location- Southern Region, Southern Capital
The only reason why Wyatt agreed to incubate the plague egg in his body was that he would postpone its hatching giving himself enough time to try and find a way to destroy it or the cure for it. However, knowing that Belphegor could just as easily hatch the plague egg even after Wyatt incubated the egg changes things— no it made things worse as Belphegor could use this as a knife to force Wyatt into doing his bidding.
When Wyatt was searching for any kind of trickery that Belphegor might have added to the plague egg he did find its connection to its creator the devil but he overlooked it believing that once he incubated the plague egg, its connection with the devil be severed and it will establish a new connection with him. This was why he was about to swallow the plague egg before Henricks and Joy arrived.