Case in point, BRL-CAD has had more than 450 years of full-time effort invested, tens of millions with development spanning over four decades. However, that investment is heavily centered around features, integrations, and capabilities that are not as typically useful to the general public.
Usability's slowly expanded, but primary paid focus is military vulnerability and lethality analyses where BRL-CAD is absolutely unparalleled. Even against the likes of CATIA, Creo, NX, Solidworks, etc., development is heavily and strategically optimized and invested for solid geometric analysis, validity, verification, and performance. BRL-CAD so overwhelmingly outperforms the commercial tools in the analysis space and is so well-integrated that it would likely cost tens of millions to stop using it.
Still, general usability is not funded and is left to the auspices of the open source community. That's a long road. Adding usability and developing infrastructure for a system that complex takes time and a level of expertise that isn't common. Until it gets minimum viable general usability, it's hard to scratch one's own itch without personal investment or extrinsic incentives.
To me it sounds like professional CAD is really hard and nobody can "just make it" in a few years of work. That's the reason why open source CAD doesn't really exist today in the professional space. But once it exists, it will eat the world. The transition phase will still take dozens of years because of all the work invested in existing platforms. We will probably see something similar to the adoption of Linux in the commercial space where it simply makes sense to use Linux instead of developing your own OS or licensing some other OS.
You mean a bit like an operating system without a kernel...?
https://wiki.freecadweb.org/Path_Workbench
My thesis is that the bigger challenge is "economic", not technical.
The value as linkdink said above is the add-ons, integrations, extensions, and the like.
It's a bit like Unreal Engine 5 having integrated the Quixel model library. You don't just get some C++ code, you also get ready-made art assets. And then you get compatibility with four game console platforms, mobile platforms, etc...
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Cad software often includes simulation stuff which requires an engineers mind.
There's no money in CAD by itself, meaning just the drawing part. Drafting is a low-value activity often performed by low-value workers who don't write software. Even if they wanted to, they couldn't make software tools for themselves. It's not like when web developers make web development tools, or when machinists make machinist tools.
CAD is sort of a piazza where the value a company gets from it comes from everything that's attached to it - reporting, CAE, CAM, etc. And they do invest in those things, often quite heavily.
It's big business to create these tools. The investment and expertise that go into them is enormous. That's why many of them cost as much as hiring another employee. They do at least as much work as one. They keep up with all the latest and greatest regulations, technologies, manufacturing processes, etc. And they give you access to a lot of valuable proprietary information.
Even if a company threw twice as much money at open source CAD, they'd still get basically none of that. They would just have an expensive drawing tool. It would be basically worthless and worth almost nobody's time.
For customers with low requirements, the less expensive tools do the job at just the right price point where it doesn't make sense to invest in advancing something like freecad.
Also, many companies in many countries are pretty much "allowed" to pirate the really expensive software. Once they get big enough, the software company will ask them to start paying some reduced amount. So there's an unofficial free tier that's way better than any open source toy.