And if you're doing it for any of those reasons, then stop doing it because you're missing the point.
Do it because you care about what you're building. Do it because you want to share your solution with the world. Do it because you want to contribute.
Of course it will. I mean, this is like saying 'making beautiful pieces of furniture won't improve your career as a woodworker'. It's always a benefit to have projects in your portfolio in any kind of skilled trade, whether done for free or pay.
Baah.. As long as you're doing a good job and writing good software, I don't give a flying fuck why you're doing it. And please don't stop OSSing because of random idealistic gatekeeping bullshit.
Hopefully they can get references out of it, some contacts, and that first 100 hours of professional coding experience. If not a job, at least the tools to get one.
OSS is a little rough for newbies because it can be pretty open ended, and having vague requirements can get us all in trouble, but it worse for people who don't have any coping mechanisms for ambiguity. Being able to close bug reports is an extremely necessary skill. Necessary, but insufficient.
There are other options like https://en.wikipedia.org/wiki/Code_for_America that should feel more like project work.
Have you done much volunteer work, and for long? I've been working off and on with such groups since I was 16, and in some ways the stories don't change for the successful ones (Anna Karenina again, perhaps?).
Volunteer-based organizations tend to end up with a small number of historians, regulars who show up and help glue the whole thing together. You get a few people who contribute intensely for a couple of years and then burn out because they aren't pacing themselves.
Then you get an army of wide-eyed energetic people who will move onto something else quickly. This is a very, very fat 'long tail' and as an organizer you have to get useful and durable work out of these people whenever you can. The names and faces keep changing on you. To do that you have to direct them, steer them into a project that is already thought up or exists but for whom not enough people are participating. Preferably something with some good optics so they feel seen (and so your organization is seen).
Because if they show up and you let them work on whatever, you get pulled in a million directions. There's no cohesiveness, no coherent story, and without those you lose your narrative, you can't recruit more people, you can't hold onto those 'intense' people who do a ton of the big work, and you disappear.
I don't know if volunteerism requires all three of these types, but it certainly gets them, and they all fill an important niche. Most of the people who are going to read your message fall into the short-timers section, and we need those although we sure would like to turn you into one of the other two groups.
This article is likely referring to mostly permissive open source, which yea allows people to profit.
We build a commons upon which better software can be built. People write open source to improve those commons, not for charity.
For me:
* I profited off free software that could have been sold as well but was not (25 years BSDs and Linux).
* I rather see my code in use because it means it solves a real problem and it does so in a good way. If I wanted to invest time into turning this software into money, I could. If I don't, why shouldn't somebody else be able to invest his/her time to turn that into money for him/her?
Why does that matter at all? What's wrong with others profiting from something that you can't profit from yourself?
Most FOSS software that is commonly used couldn't be sold for a profit by itself. It wouldn't be used if it wasn't free. Yet, it marginally lowers the cost of software development. The compounding effect of that is massive.
Despite what the GP says, developing FOSS can open up opportunities that you wouldn't otherwise have had. It's just not guaranteed.