Because a statement is your claim, and a question produces their answer. Everything you assert can be doubted, discounted, or argued with; what the homeowner says themselves — about their problem, their priorities, their criteria — they believe completely, because it's theirs. The system runs on questions for that reason, and for a second one: questions gather what statements never can.
The short answer
Compare the two routes to the same point. Statement: “You need a roof that's going to last.” — a claim, from a salesman, weighted accordingly. Question: “How long are you planning on staying in the home?” followed by “so you'd want this to be the last roof you put on?” — the durability requirement now exists in the homeowner's own words, where it will still be standing at the close. Statements position you as the seller of an idea; questions position the homeowner as the author of one.
How it runs
Statements can't discover. Every framework in the system — probing, layering, finding the real objection, isolating the investment — is a question discipline wearing a process name, because the information those steps need lives in the homeowner and only questions retrieve it. Even the objection rule “don't answer objections, respond to them” resolves, in practice, into asking. The rep's craft is not having better things to say; it's asking the questions that make the homeowner say the things that sell the job.
Spar's rounds grade your questions and your listening against the documented system — Round 1 is free, the full camp is $29/month. Spar before you knock.