It's a tad unfair on the good users who help the sites/other users by voting and answering, only to be punished for other users bad actions, or their wanting to close their account.
Answering is a major part of what the basis of the Stack sites are about - Q&A.
So to simply remove users' hard work just because another user wants out, or did something bad, is simply not fair.
Voting is also one of the main elements of the Stack system. It determines good and bad content and allows separation of the two, to allow decent content to be served more prominently. Thus making the sites as a whole better.
"Making the internet a better place.."
It's unfair on the community who help the sites and users by their good actions of answering and even those just voting the answers, to then lose the benefits gained from their actions when those very actions are encouraged and promoted by the site in the first place.
It's also unfair that good users performing positive activity lose their benefits through negative activity from the very users they were spending their time helping in the first place.
It shouldn't be possible for our positive activity and time spent to be revoked by the very people we're trying to help.
Even if not by negative activity, the point still stands that users have contributed and shouldn't have the time they spent, for free, helping others and the Stack sites simply forsaken.
Of course it all boils down to one being protective of ones assets. We are awarded for voting and answering, we feel a part of the community by answering, and downvoting that terrible answer, or upvoting a great one.
So we then feel greatly put out when our time spent, the benefits or even simply progress towards a benefit, is lost due to another user performing bad action or wanting their account removed.
The site should protect those decent users contributing in a way that without it the sites would degrade rapidly.
Two sides to a story
The other side to this is why should we gain, or progress towards, benefits from votes on a (now) non-existent question or answer?
Is rep you gained or lost from deleted content a real representation of activity you have carried out which benefits the site?
Both arguments exist and are equally valid.
However both arguments are not the same, because the counter to this argument is:
We used our time, performed positive actions, did what we're asked and encouraged to do at the time the content was present.
So, while I see the argument for removing votes from deleted questions, and agree with the reasons to some extent, I do not in any way think this argument carries enough weight to allow bad user activity to counter our hard work, positive activity, and working to ensure the site remains high standard.
Users helping the site and it's users out have no way of knowing a question might be deleted by the user or a clean up, so we should not be punished for performing the positive and encouraged activity at the time the question was live and when our actions are welcomed by the site.
As is often the case, there is likely no perfect resolve.
I don't really know enough about the system or when one loses votes etc to propose a decent and well structured resolve.
However, there are suggestions around which would make it a bit more fair on the decent users.
Mainly a change so users don't always lose all their decent activity.
I think it would be fair that any rep (votes up or down, bounty, accepted, etc) received on answers is not lost when the OP user is deleted and their questions removed.
Obviously, any downvotes on answers must also remain in order to keep a balance of what was present at the time of the question being live.
However, there must also be a way for users to still delete their answer from the deleted question if they wished, whether up or downvoted.
As changing as it is now from revoking all votes as if the question never existed, to keeping the votes present, stops users from being able to pop back and remove their answer when they realise it had X downvotes.
This would need to be catered for somehow.
Again, I don't have the answers, but it is an issue that good users lose their rep, reward progress, and sometimes actually losing privileges, from other users' bad behaviour and it should certainly be addressed.
Lastly, slight side step to the topic, I don't see why all content is removed. Is this a rights thing whereby the OP is allowed to have their question removed?
If so, I think it should be changed so, while the OP can be unlinked from the content, the question and answers should be left in place.
This would resolve the issue of rep lost and leave the question live and normal play continues (up/down votes, users removing their answers etc).
The question could simply be taken over by a dedicated Stack account - "deletedUserAccount" or whatever.