You just don't get it do you?
Not everyone has to modify the off-the-shelf frame connectors. The Hotchkis connectors I bought for my Challenger fit great. And not everyone can do the kind of work needed to fabricate their own. Even someone who is willing to do that kind of fabrication, that doesn't have fabrication experience, will take a lot longer than you did to get them made. So you don't have the "end all be all" with your example. Some people will take a lot longer than that. It took me longer than 3 hours to do mine, but I did some things with mine that involved a little more fabrication work because that's what I wanted.
And, even people that CAN do that kind of work don't always want to. I've built frame connectors and I've bought frame connectors. I don't feel one bit bad about the ones that I bought, nor do I think they're somehow better than the ones I built myself. On my Dart I didn't want the square tubing look, so I bought US Cartool connectors. On my Challenger (and all E-bodies), the rear frame rails are set at an angle to the crossmember, plus there's some floor pan height issues, making the fabrication work a little more involved. I found a good deal on the Hotchkis connectors, I liked their design better than what I was going to do on my own, and so I bought them. They look great and were easy to install. So what?
Rules organizations do all kinds of things for all kinds of reasons. Some good, some bad, some confusing, etc. As it was already mentioned, the point in this case was to keep the class evenly matched for relatively unmodified street cars- keeping out race prepped cars. Safer and stronger is great, but safer in this particular instance may also mean stiffer, which also means FASTER. So limiting the kinds of modifications also serves to slow the cars down. That particular class also has rules about what tire compounds can be run, which limits traction, which again limits speed. It's not a top end racing class, it's for owners of street cars to have some fun. Cars with more modifications, even if they are better ones, are kept out.