вот зачем

that's why

→ вот
phrase Uncommon #21,176
that's why Used to point out or emphasize the reason or purpose of something, often when the speaker has just realized it. It can also mean “so that's why” in context.
RU: А, вот зачем ты пришёл так рано!
EN: Ah, so that's why you came so early!

Вот зачем я пишу песни.

This is why I write songs.

Вот зачем Том это сделал.

That's why Tom did it.

Вот зачем он здесь.

That's why he's here.

— Чикаго (2002)

Вот зачем.

That's what it's for.

— Жизнь за кадром (2000)

Вот зачем здесь он.

That's why he's here.

— Чикаго (2002)