It's not clear to me how they pick people to lend to.
If someone is offering you a 0% APR loan, it’s either because they’re hoping you’ll move your loans to them, and become unable to leave once the 0% period has ended. Or they’re trying to sell something else (either more of something, or the same thing at a higher price), and want use consumer debt to artificially increase market demand.
You upgrading a boat, so you can save money in the long term, is literally the opposite outcome they’re looking for here.
0% financing costs the retailer 8%(ish) of the total amount, which is how the lender makes their money.
So in your case, the retailer didn’t want to lose that much of their margin.
There's also a lot of reasons one might be rejected for a credit line that have nothing to do with credit score. Some lenders have specific policies in addition to credit score, like Chase's 5/24 rule. Some are also just looking for "relationships" and won't offer you their best products unless you have a bank account with them, etc.