Using that rationale to justify not updating a product is sort of a self-fulfilling fallacy.
"I'm not going to update my product because I'm not submitting it for any tenders, and I'm not submitting it to tenders because it isn't updated".
Besides, I was referring to when the USP was still a more relevant product in their lineup. The USP wasn't designed yesterday, and there was a big period of time in between when it was designed and when the market went full-in on SFA guns that it could've been more competitive if not for the proprietary rail. The USP was designed for the military and police market, not for an incredibly small subset of nerd collectors that nobody cared about (including HK).
For the most part, USPs are not collectible pieces of history. A change from the proprietary rail (which is a PITA to even HK nerds) to a universal rail would not have been destroying any sort of collector value based on such, as there's no significant history or piece of curio to destroy. Nobody buys the USP because of the proprietary rail.
Up until the last few years, the USP was in use with a fair number of militaries and police agencies; many of the latter switching to Gen 5 Glocks and P320s as part of the move away from 40S&W and DA/SA guns. Yes, it wouldn't be very competitive in 2021 regardless, but they still should've updated it 20+ years ago when the industry settled on a universal pistol rail. I imagine there's quite a few customers who would've purchased it if it wasn't for the proprietary rail. The fact it wouldn't be a competitive pistol in 2021 isn't a good justification for having not updated the pistol 20 years ago when it was actually in its prime as a relevant product, and if updated would have had more years of relevance.