>Completely valid but how many small businesses without a security expert on board, have these in place?
Sorry to say this, but none of your examples require a security expert to implement. And frankly, they are both what I would consider low hanging security fruit. If you balk at implementing these, I question whether your product is ready for the enterprise.
>And why would it be beneficial to tell a customer about this?
This is risk management and honestly, if you don't understand risk management, you'll have a lot of trouble serving enterprise customers.
It's beneficial because in the company's mind, a legal action is a big enough risk that they want to invest resources in showing they were diligent before picking a partner.
>How could a small business deny completing this questionnaire but still get the customer on board?
There is almost no chance unless you have strong political ties to a major decision maker at that company. And, even if you do have that kind of connection, this form isn't asking for the keys to the castle.
Can your company provide a decent level of data security? How do you know?
If the answer to question #1 is not a resounding yes, you have no business trying to serve an enterprise.