Because they're with different meanings.
Come to pass means come true, realize; here 'pass' relates to 'come' ie the type 'come to do'.
>> Summer has come and pass. <<
I guess 'summer has come and passED' is better (as the original lyrics), or 'summer has come and passes' works too, awkwardly. Speaking of which, it's 'summer has come and HAS passed', so here the conjunction 'and' is just a conjunction, the word 'come' and 'pass' are both independent, like the sentence: This apple is red AND big.