It never rains but [what] it pours.
it never rains but it pours [phrase]
You can use the expression it never rains but it pours to mean that several unfortunate events often happen at the same time.
[COBUILD Advanced English Dictionary] ...............
it never rains but it pours [in British]
events, esp unfortunate ones, come together or occur in rapid succession
[Collins English Dictionary; op cit]
Obviously, the implication is that the unfortunate events happen over the same region / to the same people.