Do I have any right to know why the business was sold in the first place?

Not really, as a strict legal right — the decision to sell a business, and the reasons behind it, generally belong to the owner, and employees don't have a legal entitlement to a detailed explanation of why an owner chose to sell, any more than they'd have a right to veto the sale itself.

What you are entitled to is clarity about how the sale actually affects you — your job, your pay, your entitlements, and your terms of employment going forward — which is a very different thing from the seller's underlying business or personal reasons for selling. Many employers do choose to explain the reasoning to staff as a matter of good practice and morale, especially where it helps reassure a team that the sale isn't a sign the business is failing, but that's a choice, not an obligation.

If you're not getting a satisfactory explanation of why the sale happened, it's more productive to focus your questions on what actually changes for you specifically, your role, your terms, your entitlements, since those are the things you have real standing to ask about clearly, rather than pressing for details about a business decision that ultimately wasn't yours to make.