Why no GUI open source unarchive apps?

I know the simple answer is "because the developers want them to be" close but, and maybe my thinking is just off here, this seems like a category of project for which there would be plenty of open source apps with a GUI.

Take decompressing .RAR files on MacOS. There's The Unarchiver (proprietary) as well as Keka (proprietary). There's MacPar (proprietary). All are free (as in beer) but all are proprietary.

I get that WinZip and WinRar are proprietary because they are shareware and there's a few other paid ones on Mac. I'm curious why The Unarchiver and Keka and MacPAR are not open source. Neither Keka nor MacPAR have any association I can tell with any other company or app so it's not like they're loss leaders to get people to look at some company's other paid products. The Unarchiver is a loss leader so I guess that one makes a little more sense. Still, surprised this category of software has no open source GUI app.

I'm also not demanding they be open source. Still, I'd trust them more of they are. AFAIK they're just trojans, especially Keka and MacPAR, as the fact that they're proprietary seems to have no point which leads to trying to think of motivations for keeping them closed.

This is not a complaint. It's just an observation. It seems out of the ordinary in 2022 for a free app to be proprietary unless it has some other way of making money and in particular, un-archive apps seem like a category that would have more open source alternatives and I'm surprised. That is all.

What other categories of software are similar? Similar that they it seems like they're be plenty of open source alternatives but there aren't but for some reason there's lots of free but proprietary apps with no form of monetization?