I always found franchise initial startup costs to be predatory, as they get paid either way regardless of whether the franchisee actually succeeds. In my opinion they should be abolished and franchisors should only rely on royalties, so that they have an incentive to help the franchisee succeed if they want to make money.
As such, it is necessary to vet the potential franchisee to ensure they're going to support and improve your brand image rather than damage it. Requiring a "deposit" as such is part of this, as the franchisee will need to at least recover the amount invested by providing good service.