In the case of FPGAs it doesn't really matter that the proprietary tools are buggy. What matters is the features and utility they have. Open-source FPGA design is still extremely, extremely far behind the proprietary alternatives in many dimensions (power support, integration tools, many aspects of simulation and test, general tools like floorplanners, and so on.) That isn't because people aren't trying either. It's just really hard and has limited talent pool.

I've spent a lot of time at this point with both toolkits. I use the open source tooling extensively for my own designs. But you tell some grizzled RTL person there's no power analyzer or native SDC support or that UTM was only recently supported in some simulator, and they're going to laugh at you. They've been doing that stuff for 20 years. I know this because I've done it several times (though other people find particular things, like free RTL verification tools, much appreciated.)

I think FOSS/software people paint some very rose-tinted picture in their mind where the mere availability of something for $0 would make it an obvious choice, even at only 10% of the functionality. But that's not how people see it in reality. Many people, including engineers, think of it the other way: if it's so good, why is it $0 and how do I know it will keep being developed? They've made their peace with the fact that the $5000 tool will exist practically for as long as they need, get the job done, and be supported.