The cost of something isn't always in the form of money. In many cases with Foss there are comprises in either simplicity, stability, documentation, or compatabiliry.

For instance I can boot my machine into a live garuda instance and it runs great, but as soon as I install it, it runs like trash. I spend something like 3 hours fiddling trying to get it going then wipe and try to install smaugos and it wont even boot. I install debian and it works okay but sluggish. Popos works fine. 2 days of fiddling around and I find something that works. Windows may cost more than just money, but it worked out of the box and I didn't have to fiddle or try a bunch of different distros. We can go down that rabbit hole, but let's look at other things.

Foss often has volunteer support that can be hit or miss and often requires more advanced knowledge of the os or software. There's also often toxicity like people shaming for not knowing everything about the application or os. Commercial support is often dedicated and may even remote into your computer. I'm not saying Foss can't do that, but I've never heard of it for free.

FOSS doesn't work nearly as easily or reliably as commercial software a lot of the time. Nextcloud is a good example. There are a million ways to install it, but now you need to learn docker, or how to setup a web server and even then maybe the docker image is buggy or straight up doesn't work. The different Linux distros is another example.

Then there's the learning curve. Even if FOSS has 1:1 parity in functionality, it often comes at the cost of learning a LOT about a new application, or the functionality is different or harder to use compared to a commercial alternative.

Don't get me wrong I live foss. I self host, I'm slowly getting rid of windows and degoogling. But there is cost to do all of this, even if its not monetary. Plus not everyone has the time, patience, or interest in it.