Who says so?

If you unilaterally repudiate a valid contract, the seller could have three options:

1. The seller could treat the anticipatory repudiation (before closing) as an immediate total breach and sue for restitution, damage, and special performance.
2. Seller could urge the buer to retract the repudiation.
3. Seller may choose not pursue if such action would enhance the damage.

Under 1 and 2, the seller could force the house sale through court if he wants. I doubt if anybody knows the law this clear to pursue this option. Most times, seller will choose to sell the house to somebody else but hold you liable for the price difference if the the selling price is lower the second time. Downpayment is for sure gone. In Cohen v. Kranz (NY 1963), the plaintiff wanted to back off the house deal because the house after inspection was not built according to the building code, thus, the title was unmarketable. The defendant seller sold the house to another buyer for $1500 less. The court said the defects were small and awarded the seller $5000 downpayment PLUS the $1500 price difference the seller would have been entitled to.

Technically, the worst case is that you would have bought the house anyway. If repudiation after closing, that is an immediate breach and the seller should have the same three options.