It's not. It's a reminder that all of your sales and marketing efforts are wasted if you're not actually pushing towards a sale. Calls to action, follow ups, using funnels—all of these are things that increase an individual's likelihood to close. That's "ABC".

Try to close too early and any sensible customer will run away and never talk to you again.

"Always" be closing includes too early as well as too late, after the client has run away and you will gain nothing except to alienate him further.

Yes, a three-letter acronym is incapable of expressing every nuance of a complex interpersonal dance. ABC is about sales and marketing driving towards the close. It doesn't mean you turn a cold call into "Hi, my name is James, buy my product. This is what it does. Buy it. Do you want to know more? Buy it first."

It's "closing" because, from memory, they're selling junk real estate. In the US, the end of a real estate transaction is called closing, beyond which it's (mostly) irrevocable.

Hence Baldwin is effectively saying "get to the end of the transaction."