Why do people say “God bless you” when people sneeze?

There are a lot of myths surrounding this practice but the one that kept reoccurring in my research is the following:

In English-speaking countries, it is common for at least one person to say "Bless you" after someone sneezes. The traditional explanation for the custom is that it began literally as a blessing. Pope Gregory I the Great (540-604 AD) became the Pope just in time for the start of the plague in 590 AD (rumor has it that his predecessor died from it). To combat the plague Gregory ordered everyone in the land to pray for God's intercession. When someone sneezed, they were immediately blessed ("God bless you!") in the hope that they would not subsequently develop the plague.

From there, it just became a custom to say “God Bless you” whenever someone sneezed!