I don't think this saying applies to the situation you are in. Perhaps more apt is "you get what you pay for".

For myself, I've switched to paying for Linux and open source software. I believe open source needs to be sustainable for consumers and expecting devs to work for free is insane.

Since I didn't pay for my previous Linux, it means that I didn't get much for it, right?

it's just an analogy

That saying is meant for commercialized products obviously. But it's still kind of true if you stretch it to FOSS software, the allegory would be that you pay for it with your time (by fixing/bringing attention to bugs) rather than directly profiting the devs.

I pay for my mobile phone service. They still sell my location data.

I pay for my TV. It still spies on me.

And so on...

You are always the product, paying customer or not.

You are sometimes the product when you buy something, but it's not a necessary part of that model.

You are always the product in "free" services like FB, YouTube. It is a fundamental part of that model.

There are plenty of shitty companies in both buckets (and seemingly more as time goes by) but let's not pretend there's never a difference.

I'd be happy to see such a counter example. If something can phone home, it will. I've yet to see a purchasing site (= I am the customer) which does not share data with third parties, for example.

How about Fastmail or Posthaven?

A better phrasing would be "you don't get what you don't pay for". The mere fact that you've paid does not guarantee that you receive anything of comparable value in return.

When it comes to open source and other community-based projects, it's true that you shouldn't expect much in the way of personalized service or attention to your particular needs or issues if you're not paying for it. Fortunately, just making a copy of some software (even really good software) doesn't cost much at all, so it's not unreasonable that you're getting that much for free. Improving the software requires an investment from someone, though, one way or another.