Because that's not how people work - if they were refundable then he would get many more deposits and may spend that money, but then the flaky people will want to refund those deposits and he might not have the cash reserves to pay them, thus having to declare bankruptcy and liquidate the company. And people might refund deposits for any reason - they decide they want the money for themselves at that point, or a spouse dissuades them from buying a helicopter now, or they just get impatient and decide to buy another helicopter or retain their current one instead.