When a company does not approve your request before it expires, which is based on the event deadline date you've set and/or the company's own minimum lead time relative to the event date, the request is automatically canceled for non-response.
Similarly, if you receive an offer and do not accept it prior to its expiration and/or cancellation of the offer due to reachig a desired number of responses, the offer may be automatically canceled as well.
It is typical for companies who receive many more requests than they can approve to let requests they cannot immediately answer sit in their queue, in case they are given the ability to approve them later. When this isn't the case in time, auto-cancellation happens.
In general, items that will be shipped or delivered typically have longer lead times, although some companies simply prefer to make decisions farther in advance. Desired lead times may be communicated on company websites or in donation profiles.