People still pay for customized software. Each company has some internal weird corner cases that are not covered by standard open source software, so you can sell the customization to them or be an employee that does the customization internally.

In a recent project I used standard libraries to connect IMAP, SMTP and web scraping. Nothing interesting. Just connecting tubes and a regular expression in the middle. And a for loop, to repeat it. Nothing interesting, but it's enough to be the computer wizard.

Yes, thats my observation too. While sometime you find libraries that can be bought (e.g. ExtJS), there is no real market for libraries as everybody is used to use open-source, pay nothing, and adapt it to their needs.

I quite liked extjs way before single page apps were bastardised into flying spaghetti monsters. It makes more sense than react but many struggled with basics such as function scopes and jumped the bandwagon. Whereby in extjs you can structure your js app in react you create a mess. But its free, and cheap corps prefer free labour.