The months which pass between submission and response can seem terribly long and I’ve heard all sorts of desperate reasons offered for that long delay. Some writers insist that agents don’t bother to pay attention to the slush pile because they hold all writers in contempt unless they’re top-selling celebrity types: that’s a great slur on agents who are, on the whole, committed, passionate professionals with great talent, scope and flair. One particularly embittered individual insisted that submissions were purposely not returned for several months in order to give the impression that the agents were busier than they really were: the logic of that one, coupled with my own experiences of slush, left me reeling.
The best editors and agents tend to be very overworked. Both jobs require a lot of reading, which is very time-consuming; and they have to prioritise clients and books which are already under contract and which they depend on to earn their livings. Reading through slush is purely speculative and very unlikely to earn them anything at all and consequently, it can’t be given priority.
Here’s an excellent account of how much effort one particular agent makes to clear her slush pile, from Rachel Vater from Folio Literary Management: she’s an established, successful agent, and describes the problems far better than I can.