Nope.
I do this as a hobby, not a business. I do some fabrication work on my own cars, but there’s a big difference between doing some one off fabrication for yourself and doing any kind of fabrication for production.
Sure but the case you’re taking about was a car that had torque boxes. Without those none of that extra work would have been necessary. That’s true of pretty much any part you buy for these cars, sometimes modifications are needed, sometimes they aren’t.
And there’s still a decent difference in the amount of work and skill it takes to make some minor modifications to an existing part compared to fabricating something completely on your own.
If someone wants to buy their connectors, what difference does it make to you? Sure, you can make them yourself if you have the time, skills and equipment. And if you do that you may save some cash, although probably at the expense of your time. Which is fine if you have the time and the desire to do it. But if you don’t, so what? Heck, even if you do have the time, skills and equipment it doesn’t necessarily mean that fabricating subframe connectors is what you want to do with that time.