One of the things I always forget is how much harder it is to rack up words in a proposal than in a novel — each word has to count for so much more. A good proposal is only five to ten thousand words long — sometimes a lot less than that. In five to ten thousand words you have to present a novel that may run 150,000 to 200,000 words; you have to do it in an entertaining fashion that hits the high points and permits people understand the story and love the characters; and, you have to convince a publisher to part with enough money to feed you and your family for a year or two, and if you’re lucky to do so in a prompt fashion.
A proposal is not a short story — it is a compressed novel. They’re a pain in the ass to write, and I don’t enjoy doing them. But, and this is a really big but, it’s a lot nicer to do the proposal and get money up front than to write the whole novel on spec, and hope after you’ve written 150,000 to 200,000 words that someone will buy the damned thing.