Ok, then... tell me. What browser do you use? Do you have a cell phone? Is it an Android phone? Because I guarantee you that unless you're still using Internet Explorer and have an iPhone, you are using open source software. The Chromium engine used by both Edge and Chrome is open source, with Google as the primary contributor. Some interface elements are proprietary but many of them carry over to full FOSS Chromium browsers like Opera and Vivaldi. Well, what about Firefox? Also fully FOSS. The basic framework of Android is an ARM-compatable fork of Linux.

I've found LibreOffice to actually be EASIER to use than Microsoft Office, and on top of that at this point Microsoft Office formats are almost perfectly supported. The only thing that doesn't carry over is scripting because LibreOffice uses a different scripting language from Microsoft Office, but in this day and age I guarantee you that 99% of people don't even use that anymore.

Are you in software development? Do you work with Java? Chances are, unless you work for a big megacorp, your company switched from the Oracle JDK to OpenJDK. Which, by the way, has Oracle as a major contributor and a mirror host.

Sure, there are definitely examples of open source software that are a bunch of crap. I've yet to find a good FOSS CAD program that has compatibility with .sldprt and .sldasm files, acceptable compatibility with .step files AND a decent interface. But most of the stuff I've used has been more than adequate.

One thing you have to keep in mind is that open source developers typically "eat their own dogfood" (meaning that they use the software they develop). Chances are if they made the UI bad enough that it affects their workflow, they're going to change it so that it's easier and quicker to use. So they might not necessarily be getting feedback from users (although that's very rare, most open source projects maintain community networks that rival or even surpass corporations.) but they're actively field-testing their software. And on the flip side, big corporations don't actually give a shit about the user. If they can get away with saving a quick buck and hiring "Bubba McGeoCities" to do their UI and still get their product to sell, they will. And they won't change it if a handful of people complain that it's completely unusable as long as it still sells. Want to know what the worst software I've ever had to use was? QuickBooks Online. And it very much felt like the combination of a late 90s GeoCities site AND Baby's First Tax Software. It makes a TON of costly mistakes (the IRS will not take "But QuickBooks said I owed X" as an excuse for an incorrect payment) and if you try to fix those mistakes the software actively tries to "correct" them back to its original, incorrect output.

As for the "freedom" aspect that gets mentioned a lot, that actually refers to the software license. Most open source software licenses give the user the freedom to copy, modify and distribute the software, with the only requirements being that the license cannot be changed with your distribution and the original developer must be accredited. The GNU GPL also requires that any other licenses used for various libraries and plugins must also be GNU GPL or similar. On the flip side, there are licenses that eliminate even the "share alike" clause, and one that outright says you can, and I quote, "do whatever the fuck you want".