It's quite hard to gain traction on a corporate sale and you're right that keeping the customers and the consumers in the dark is 'par for the course', but to withhold the name of the company from an interested party serves only one goal.

Think about it: I have this company for sale but I won't tell you which one it is until you sign this document.

What's is there to lose for the company to have its name spread to those that might be interested?

It's not like they're advertising the name in the NYT or making it public other than on a one-to-one basis with leads and those leads are definitely not going to publish the name if they're really interested because the last thing they need is more interest from others.