In my experience, terms like "framework" get overloaded and can mean different things to different people/roles/job titles. I tend to use "library" when talking about commericial or open source tools like Selenium or Appium, as they are a collection of APIs to use to build test automation, which is a framework or collection of tests to perform against an application.
Other people tend to use "framework" to mean commercial or open source tools like Selenium/Appium. This is all semantics and open to interpretation and is context dependent. I tend to not let terms like this get in the way.
To answer your question, no, it's not required by tech companies to build a custom framework. However, some tech companies justify it from a business perspective instead of a technical perspective.
One reason I've seen among companies that do this is that if you as an employee have to create or learn a custom system, it makes you more employable to that company. Companies want to do things that retain employees as that saves them money versus having to hire and train someone new, which costs money. From the employee perspective, this can mean it might make you less employable to other companies, which keeps you at the original company.
Another reason to use custom test automation is maybe this company is building bleeding edge software/products that haven't been created before and there is no other viable alternatives. In this case, they would need to create something custom for their needs.