You send the proposal on a Thursday. By Tuesday there's nothing, and you start filling the gap yourself.
They hated the price. They've gone elsewhere. Someone senior read it and winced.
It's usually none of that. The person you sent it to isn't deciding. They're waiting on someone who hasn't opened it, who is waiting on a budget conversation that keeps sliding a week. Your proposal is sitting exactly where you left it and nobody is arguing about it at all. That's the part that stings more than a rejection would.
Which changes what the follow-up ought to be. "Just checking in" asks them to report a status they haven't got, and it arrives as a nudge about your quarter rather than their problem. So they leave it, and now there are two unanswered messages instead of one.
The follow-up that works gives them something to forward. A one-line answer to the objection you know is coming from the person who hasn't read it. A single revised page for the bit that wobbled in the room. Something they can paste into a message to whoever is actually holding it up.
And if you can't think of anything worth sending, that's useful information about the deal. It generally means you never found out who has to say yes, and the proposal went to the person who was easiest to talk to.
Silence isn't a verdict. Most of the time it's a diary.