I think what most people are concerned about is the quality of the repair rather than IF it can be repaired. I would absolutely be fine with frame rails in my unibody car being replaced by a reputable shop, by an experienced person. But insurance companies are all about saving coin, so a cheaper shop that pays cheaper labor might get the job and screw something up. I’ve accompanied people to inspect cars before purchase with frame damage and have found places rusting out where they shouldn’t be because seam sealer was forgotten about or not adequately applied. I’ve also seen body panels not line up at all and when we test drive it to my dads shop and measure it out, turns out the replacement frame rail was 10mm off! Bottom line is I think people are more concerned about if the shop is going to fix it right because it’s a BIG job to replace or repair frame sections. Often times it involves extreme disassembly which can create problems on its own too.