Because the Greek word means presence and not coming.
And they would not ask Jesus what would be the sign of his coming as they would not need to if he was coming visibly. They could just see him.
They knew that Jesus does not come back to earth. No reason to. But people think that they are so important that they want Jesus to come here with them. That is about as arrogant as their believing that they go to heaven to be with Jesus.
"after reading Matthew 28:19, 20." Are you sure that Matt 28:19 is proper considering that 1 John 5:7 added the trinitarian formula. How can one know that Matt 28:19 is correct in that manner?