Wow. I don’t know what kind of companies you’ve worked for, but that is exactly the expectation everywhere that I’ve worked. Company computers are for company work with company software, and that’s all. A small amount of personal email or web access might be permissible, but installing software not licensed to the company is strictly forbidden. This is for several reasons, namely, security and legal protection from pirated or unlicensed software.
In the age of smartphones, there’s almost no reason an employee needs to perform any personal tasks on company IT assets.
They were more concerned with company data being copied outside the company. That’s why you couldn’t write to any USB device, and all emails sent were monitored for keywords, such as social security numbers and account numbers.
You could send such data to customers for business purposes, but you had to encrypt it. The customer was directed to a web page to decrypt his email.
As for software, never mind it being licensed to the company. Your supervisor had to approve it and say it was necessary for your work.