I don't want to derail this thread by continuing down this dark path too long but remember fishman ESB was the second film to be released.

So at the time we, the audience were under the impression that Vader murdered Luke's father (and not Hayden Christensen with his evil Master Darth Lucas).

It's only after Yoda confirms the revelation given to us at the end of ESB in the next film that we know for sure why.

It does seem a bit silly that Vader would just give up on the chase when he has a clear lead.

Palpatine wants Vader to put the willies up Jerjerrod but that wouldn't stop him from deferring the search duties to his task force.

The Emperor was all for it in ESB and seems to only pull Vader off the deal when his convinced Luke will seek his father out himself.

If anything Palpatine is using Vader as a self baited trap for Luke (and Vice-versa) but that doesn't happen until after he rescues Han.