Why does it take so long for survivor claims to get answered?

I assume you are referring to a claim from the Veterans Administration. First, have you checked the status of your claim online with the VA* (if you filed it with through a VSO, contact your representative)? The VA processor will update the claim in the system (which you or your VSO representative will be able to see) every time there is an advancement of it.

There are a multitude of possibilities that can delay a claim. Everything from the type of survivors claim (DIC? Death Pension? Accrued Benefits? Etc.) and how much information the VA has to gather to the backlog of the office that is processing the claim.

If you submitted a claim that was straightforward and had all the evidence to prove the necessary elements of the claim, then it would just be processing time (i.e., dependant on the backlog of the office). If information that cannot be verified readily, there are judgement calls involved, or it's a complex claim (if A and B happened, but not C, and only if D or E occur in the preceding year...) then it could be much longer.

All VA claims GENERALLY follow the following process:
● The claim is received by the VA regional office
● An initial review of the claim is conducted for accuracy/completeness
● If there is any missing evidence for the claim, the VA will attempt to gather it
● Once all the evidence has been gathered (or all attempts to obtain it have been exhausted), a review of evidence is conducted by the claims processor
● All this is put together in a decision packet that could be straightforward or has to go through multiple reviews if it's one of the later type of claims described above
● When it finally makes it though all that, you will be notified of the decision
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* https://www.va.gov/resources/how-to-check-your-va-claim-appeal-or-decision-review-status-online/

I once checked the status of my claim, "they" wrote: "You are number 67,000 in line". Many moons later I received an answer. You are dealing with the VA - don't hold your breath.

Go online, check the status of your claim. This will give you some clue where you stand.