To be a host on Skynet, you have to declare yourself on the Sia blockchain, which means users running a blockchain node (full node or lite node) are able to have a complete and limited list of all the possible hosts on the network. The Skylinks aren't just hashes, they contain a couple bytes extra of information as well.

Between the explicit list of potential hosts and a small amount of hinting in the Skylink, you can narrow down the number of potential places a file is stored to be small enough that you can just ping all of them in parallel with a request for the data. You don't have to do any multi-hop routing to find the data.

This saves latency.