Why does it ask about people who own 25% of the business?

Financial regulations require the processor to identify beneficial owners at that threshold. If you are the sole owner, there is nobody else to add.

What it asks for

Your business: how you operate (in your own name, or through a registered company), the legal name and structure if it is a company, the name you do business as, address, phone, website and what you do. If you rent out property in your own name, your legal business name is simply your own name, and your SSN is used if you have no EIN.
You, as the person in control of the business: name, title, email, phone, date of birth, Social Security number, home address and how much of the business you own.
Anyone else who owns 25% or more of the business, if that is not just you.
How you will take payments: your business category, the name shown on payers’ statements, and estimates of your volumes and typical and largest payments.
The bank account you want to be paid into, and your agreement to the fee schedule and the terms.