Could you imagine the traffic it would generate if an estimated 30,000 LimeWire nodes sent out queries every half an hour for each file they are downloading? Let's assume each node is trying to download 10 files, that would make 300,000 queries every half of an hour or 10,000 queries per minute. Can your connection handle 166 queries per second, when each search query + search results is - let's say 100 bytes? (That would make it ~16k/s in BOTH directions just for receiving and forwarding other people's searches). Ultrapeers would have to drop connections to cope with the traffic, which increases the distance between the nodes and your search queries can't reach hosts that are far away.

That's why the time between requeries is set to a couple of hours. The amount of search results you receive are (simplyfied) inversely proportional to the amount of search traffic each client generate.

If it was possible, the LimeWire developers would certainly reduce the time between requeries, but at the moment that would be extremely counterproductive.