There is a PITA factor in having multiple accounts. They each need to be tracked and monitored, records kept and fees paid. This doesn't sound like much and it may not be an issue for someone good at managing details, but it can be a problem if someone else needs to step and manage the finances in case of illness, accident or worse. We have simplified some since my ER and I continue to look for ways to reduce the number of accounts, and have also included instructions on how to do even more should I leave the scene unexpectedly.
I think for most retired people one investment account and one bank is enough. Working people need to deal with employer provisions that complicate that.
+1 Vanguard and local bank