My experience has been two extremes:
1) companies that use open source, modify it (to the extent that it's largely proprietary), and deride the open source community that competes with them
2) companies that use open source to leverage non-core functionality they need... and move on with their real value-add
Companies in the style of (1) never contribute back. They see open source as the competition, even though they use it themselves. They don't understand that proprietary extensions are just that... proprietary software in a non-expertise area, that no one else in the world knows anything about. Instead, they spend more and more money "fixing" things which were already fixed in the upstream releases years ago.
Companies in the style of (2) contribute back minor bug fixes or features which are pain points for them. They sometimes pay for other people to write new features.
I say this as someone with 20 years experience working on both sides (corporate / open source) for companies doing both (1) and (2) above.
0) Companies funding the full development of large OSS projects. Examples: MySQL, Postgres, nginx, Chrome, Tensorflow, React, (Most of) Linux, Redis etc. etc.
That’s not to say startups don’t contribute, but my experience is that a lot of startups—usually led by inexperienced managers—see contribution as giving something for free instead of charging. Small-minded nonsense indeed.
Small-minded, no doubt (though "business"-minded rather than specifically startup).
In my national context (Australia), the vast majority of companies, small and large, operate purely in the fundamentalist capitalist mindset. There is no 'should' (conceived ethically) in their stock of concepts. It literally doesn't exist (where it occurs it's just a PR exercise, which the PR department will translate into management's native dog-eat-dog language for their comprehension in meetings).
Ideally we wouldn't work for such companies. But the stock of jobs at better places is limited, so by statistical definition 'most' of us won't be there.
Now they could be donating some amount of money, but that's in no way required.
Do they ever do any actual work? Because every company I've seen or worked for has wondered just how they have the free time to do all this stuff with bill paying client work to attend to or a product/service to maintain.
Or do they simply have a one hour work week like a fictional character would?
If you did, you'd have found a way for it to work.
Making a pretty cool deploy script? Document it and put it out there as OSS.
Making a class/module to sort items semantically? Make it OSS.
Someone made an IDE extension to syntax highlight WebVTT files? Make i OSS.
Made a file lister/selector for JQuery? OSS.
Integrating 3rd party X with 3rd party Y? Opensource your module for it.
Unless all your developers do is hack stuff badly together in a monolithic mess, some of it can be opensourced.
If you spent 1/10 of an engineer on an open source product, and 100 other companies do the same, your company gets much more than it puts in. And because it's open source, you know how to fix it, and you can fix it.
I know of multiple billion-dollar companies who can't get the time of day from Cisco, HP, etc. for bug fixes or new features.
The vendors attitude is: Bought 10M of product in the past year? Meh... piss off. We're working on important customers.
The rest of us have work to do.