Technical reasons aside (some of these vendors are on 20+, even 30+ year-old codebases by now), the other big reason why they are making the "wrong" product is that the "right" product avoids some vendor lock-in and makes some of the consulting market redundant. As far as the product managers are concerned (or, more accurately, as far as the metrics based on which they're evaluated are concerned), the "wrong" product isn't wrong at all.

End users have been complaining about all these "20 thousand GUI-based idiosyncrasies " forever, but they've nonetheless put up with them because at the end of the day you have to ship the damn thing.

There's been no shortage of outside players attempting to "disrupt" this market. However, most of these attempts have been comical failures. Instead of addressing problems that FPGA/hardware engineers have, lots of these attempts were focused on addressing the sort of problems that software engineers have when they try to do FPGA development. Not necessarily (but, in some cases, also) due to sheer superficiality, but also because they are problems that are a lot more accessible when coming from outside the field, without a foothold in the FPGA manufacturing/development space (i.e. when you're not building tools for FPGAs that you design, manufacture and sell).

So lots of these problems are very much WONTFIX: users have no meaningful alternatives, and fixing some of these things might actually even make it easier for alternatives to spring up (or at least for users to build various in-house tools that aren't so vendor-specific). Why would any FPGA vendor waste money on that?