Lots of possible reasons, including:
1. Buyer couldn't ultimately obtain financing after closer review by underwriting
2. Latent defects were discovered during the home inspection, and buyer didn't want to assume the risk/responsibility of mitigating them
3. Seller was unwilling to resolve issues discovered after inspection
These are just a few potential reasons that result in the "end" of a sales transaction. Without knowing the details of your transaction, it's impossible to speculate on exactly what happened with the property in question....