When using ‘how come’ you are asking why a particular thing has or had to take place.
Here are some examples:
“How come parents worry so much?”
“How come people carpool to work?”
“How come you are so upset?”
“How come he will not call you?”
“How come you stayed out so late?”
“How come you cannot make a decision?”
“How come you always question me?”
“How come we never agree?”
“How come your dog digs in the yard?”
“How come she will not come over?“