Generally speaking when purchasing a business, the buyer is only going to want to acquire the assets of that business and not buy the actual business entity. Why not? Well, the entity could have unwanted characteristics or hidden liabilities. For example, if the previous owner made a mistake on a tax return, that mistake could lead to thousands in unexpected tax liability, penalties and/or interest, which the new owner would not want to incur.
There are circumstances where an asset sale is not the prefered purchase method. Typically, those are situations where the business entity holds a license that is non-transferrable, such as a liquor license, or the entity has a non-transferable contract, such as a government that took a long time to bid and be awarded, but for most transactions, an asset sale is going to be the preferable form of purchase.