All it takes is one website to poorly secure your credentials, and your password is exposed everywhere in this case. Use a password manager, and use the max length you can for that website.
In my keepass DB, I have 295 passwords. Are you suggesting that I should manually remember 295 unique complex passwords, rather than one long, secure password (that I cycle every 6 months or so), and a 2 factor key?
Also, my password manager protects me against phishing attacks such as being sent a password reset for my iCloud account, and clicking on the link to icloud.malicious.com. if my PW manager doesn't fill it in automatically, I don't give it my credentials as there's something wrong.
You also imply that value is a fixed cost. For instance, in 2008 when I signed up to facebook, it was a low value account, now it's a high value account.
The problem with "remembering" multiple different "easy to remember" passwords across multiple cites is that there is a limit to how many "the password for site X is Y" associations you can hold in your head before you start forgetting which password belongs to which site.
Just use a proper password manager, then you can have proper randomly generated passwords that do not each need to be remembered (and their association to a site remembered as well).
