@idm, your suggestion would create problems when copying sales quotes to other transaction types. The customer field is reserved for defined customers, because they are actually subsidiary ledgers of the Accounts receivable account. They are not just names in a space. Even if the name were to be picked up from an address field, other information needed for customers would be missing. And the customer name would then be duplicated on other forms where the real customer name and address appear together.
The point of customerless sales quotes, as described in the Guide, was to accommodate the kind of one-off quote you would never expect to go back to or search for. The process was described in response to users who are swamped with many quote requests, so few of which will turn into orders that creating customers is not thought to be justified. In other words, if there is ever going to be a reason to look up the quote in the future, you should define and use a customer.
Nevertheless, you can overcome your problem by mentioning the customer’s name in the summary-level description field on the sales quote. Contents of that field appear in the Sales Quotes tab and would be searchable. For example: