I'm not a security engineer so pardon me this is dumb.
From what I understand, password managers stores all your passwords in hashed format and uses your "master password" as the encrytor.
master password
H(password) <----------------> encrypted password
The key difference here being that this is two way hashing so passwords can be decrypted.
In reality, there are a lot of attack vectors like MITM, event logging or sometimes straight up storing data in plaintext. Through these hackers can generally get passwords of all users of these services.
So, why don't people use local password managers?
Just a txt file encrypted with "master password" should be pretty damning to break into. And the reward for breaking in would be password for 1 person. (compared to 100k businesses).
Obviously, this would be less convinient and wouldn't sync between devices. But would do the job.
And the best part is there are solutions already that do this: https://keepass.info/
So, why do people and companies use Okta, Lastpass, 1pass etc?
Allowing convenient use of strong, unique passwords per-account IS the job. If a user can't quickly access their passwords on all their devices, they're going to fall back on just typing it in. And in real life, that means they pick easy passwords and reuse them in lots of places. This opens them up to attackers who either guess the password, or take a password learned from one site and try the user's accounts on other sites.
A great password manager does the following:
1. Makes it easy to generate strong, unique passwords per-site every time an account is created.
2. Applies an expensive key derivation function to your vault password to make brute force impractical for all but the weakest passwords, so that stealing vaults is of minimal value.
3. Does not ever transmit your vault password off your device, so that an adversary who can intercept every vault file and every plaintext byte of traffic going to and from the server still cannot do better than a brute force attack against the vault.
4. Does all 3 of the preceding with a rigorously designed process that is regularly audited by multiple experts, and actively monitored to ensure that these things really are happening throughout the lifespan of the product.
5. Syncs across devices and integrates very well with the browser so that users have no incentive not to use it.
Lacking any one of those elements greatly compromises effectiveness. Homebrew solutions can be pretty dodgy about all of them, and #4 and #5 are particularly difficult even with a large budget and staff.
I'd say Bitwarden and 1password have earned excellent reputations for doing all 5 of these things. LastPass's reputation is not so great.