Collecting and/or accounting for financial assets spread across numerous entities is a nightmare, as you can attest. It is especially difficult when there are numerous heirs and some of them claim ownership of this or that. "Mom promised that $5,000 Ming Vase to me!" - or the cabin by the lake, or the trust account with the special fund in it, ...etc. etc. I had a situation where it just happened that I was the one broker the executor (her oldest daughter, in this case) trusted more than the others, and asked me to do the consolidation of funds and all that. I had to set up several new accounts, Inherited IRA's for her and her siblings, etc. It wasn't too horribly bad or difficult, but it was time consuming as hell, and her brothers and sisters were spread all over the country.
The fact is and remains, the more money and accounts you have, the more important it is to have one or two trusted people who are aware where everything is squirreled away.
Not to speak for Progree, but one reason I have found for clients that did that was the old "Don't keep all your eggs in one basket" idea that some folks from our parents generation took VERY seriously, particularly if they were children of the Great Depression.
I think many Americans born in the 20's never got past the knowledge that before the FDIC came along in the early 30's, individual banks could and would fail all the time, leaving their customers penniless. Keeping accounts all over town, so to speak, was safer in their minds, by spreading out that risk.