why would someone pay for this when they have access for free in a supposedly less buggier interface?
Have you never heard of "advertising" ?
Because VC money
A less buggy interface for some is unintuitive or too generic for others.
Why would someone pay for dropbox when they already build such a system themselves quite trivially by getting an FTP account, mounting it locally with curlftpfs, and then using SVN or CVS on the mounted filesystem?
Because people just don't know it exists? ChatGPT is a open box. ChatGPT wrappers are real apps.