This is absolutely insane to me.
The number of people reporting needing access to multiple hundreds or more of required credentials is blowing my mind. If this is the reality of how people are using the internet these days then we desperately need a better cross-platform solution to identity management and authentication than can ever be offered by passwords. These vault programs are sounding more like a horrendous bandaid than the mere unnecessary convenience I viewed them as.
If you need to share passwords amongst multiple people I guess I can see some of the appeal of these networked vaults, but it strikes me that even this is a drastically subpar situation that ought to be handled on a deeper architectural level (like with sub-accounts and ACLs).
What's absolutely insane to ME is how consistently your responses seem to ignore that other people have different use cases for passwords. Nobody cares if something seems "insane" to you. It may surprise you to discover that services like these exist, perhaps, because people interact with passwords in a different way than your "I only keep passwords that I use monthly" brain database paradigm.
I mean, this is all apples and oranges, but if you could, examine your browser history across all devices as a household going back let's say 10 years. Lots of sites, right? How many did you ever create an account on for whatever reason? Are those all in your vault today? They essentially are for us. To the very best of my knowledge (and there's functionality in 1Password to analyze this, obviously anything not in vaults is invisible to it however) we have no duplicated passwords, anywhere on the internet.
To give some examples of how we do use 1Password, in terms of "Online Shopping" (just one of our shared vaults) that has 100's of credentials for everything from Amazon through Walmart and covering whatever we buy online from groceries to ammunition. Tons of more specialist or niche suppliers like Christmas Designers also make you 'Create Account' to have order histories and to be able to track shipments - this one in particular is a great place for garland, lighting and other holiday items, tis the season!
1Password also stores all our rewards programs (i.e. Store Cards, Airline, Hotels). I'd guess we are signed up with 40-50 merchants for some kind of "Rewards" (i.e. Fred Meyer or QFC, and where the ROI for signing up for their program is some items will be $2.49 instead of $4.49 on offer). I have traveled a lot for business and so can't always fly one carrier alliance or stay entirely within one hotel chain, so I guess that's another ~20 (airlines) and ~20 (hotel chains) for you.
I'm not going to memorize software licenses (serial numbers or license files for e.g., Bartender for macOS), nor other access tokens (i.e. SSH Keys, API Tokens) to various geekery.
Two other things which end up helping a lot, one of which adds lots of vault items: the integration story with Privacy [1] and Fastmail [2]. We've used and loved Privacy for a long time, and this integration stores the unique per-merchant credit card details in a vault. With Fastmail you can create 'Masked Emails' so you've got a unique email for each place you signed up. We've easily rotated both card details and emails on accounts when we find out someone was compromised, and with these integrations we're only rotating that site, not potentially 100+ sites using say the same Chase Sapphire card.
I am entirely happy for my family to just have access to the Amazon or Netflix email addresses (logins) and passwords without any of that overhead.
Like you we have TONS of credentials (and other supported items), around 2800 vault items in total, some of which we definitely only use once a year, others we use multiple times per day. Probably started using a password manager and some technique to share some vaults around 2010, so also a decade.