🕆 How Come?

‘How come?’ is a colloquial substitute for ‘why?’. It is used to make questions.
I can say, ‘how come you didn’t go to the movies?’ as an alternative to ‘Why didn’t you go to the movies?’.
Notice how they are used differently

How come you like football? –vs – Why do you like football?
How come you went to London? – vs – Why did you go to London?
How come Joe can go? – vs – Why can Joe go?
How come Harry is coming? – vs – Why is Harry coming?

(How come Harry is coming? can be contracted to How come Harry’s coming?)

How come he’s got the big piece? – vs – Why has he got the big piece?

Did you notice the differences in the grammatical structures?

When we use ‘How come’, we do not need the auxiliary verbs DO; DOES OR DID. The sentence is structured like in an affirmative sentence. And notice how the verbs that normally use inversion to make questions do not need to be inverted (like BE and MODAL VERBS) with How come questions.
How come is not used in compound tenses using HAVE + past participle and neither with most modal verbs
How come John can/could go? ✓ but ‘will, must, might, may, would, ought to, shall, should’ should not be used with ‘how come’