There is at least one reason: clients do not always know (or care to know) who is actually doing the search, and this points to a significant problem. Even if they cared, how would a client know if the search was done by a highly skilled specialist or by a low-skilled searcher? Price and location aren't enough to qualify a searcher, and local expertise is easily claimed and currently almost impossible to verify.

Couple that with the possibility that clients may not even value searching as a high-skill activity, and this presents a significant market dynamic that will continue to exert a downward price pressure - especially in counties that can be done 100% online.

Essentially, a search vendor can hire a low-wage (domestic or offshore) employee, significantly undercut the market and still make more money than by using an independent local searcher. None of this would be visible to the client, and it is likely that no one will care. As long as the client is comfortable with the risk (and they can transfer some or all that risk to the search vendor) this situation is unlikely to change.