It's entirely possible that they couldn't. Let me explain, as someone who has had to deal with the financial affairs of other family members multiple times.
First, not everyone keeps their financial affairs well-organized. For every person that has a neatly-labeled box of file folders, there's one who has thrown important papers into random boxes along with old newspapers, magazines, and junk mail. LOTS of random boxes. So merely trying to answer the question "What accounts does this person have?" takes a lot of work and a lot of time -- and even if that work's done carefully, it might still result in omissions.
Second, some people keep their financial affairs on a computer/online, which means that someone trying to help has to work through all that -- all the security, all the ID verification, all processes, all the bureaucracy, everything. This can be brutally difficult: it means hours and hours on hold with customer service departments that want to avoid doing anything resembling service. It means endless letter exchanges. It means retaining an attorney and getting documents notarized. It means sending things overnight recipient-signature required and then being told they never arrived. It means filling out forms and submitting them only to find out that they're the wrong forms -- even though they were the ones you were told to submit.
Third, it means dealing with people whose only goal is to get your problem off their desk and out of their queue -- so they'll close help desk tickets without bothering to ask if the problem is actually solved or even bothering to inform you. (When you call back, you'll be told that no such ticket exists. When you insist, they'll tell you that it was resolved and thus closed.) If you somehow manage to get past this, you'll be told things like "our anti-fraud procedures prevent you from paying your grandmother's electric bill" -- yes, really. Or -- and I'm not making this up -- "we need to talk to your mother directly". Oh? My mom? The one whose death certificate I sent you four months ago? The one whose leftover $2.17 cable bill I'm trying to pay so that I can close the account and never have to speak to you again? That one?!
I could rant about this for pages, but the bottom line: trying to step in and handle someone's financial affairs is a full-time job. It requires constant attention, endless phone calls and letters, and a mountain of work.