Again, it's a tradeoff
Of course, it would be better to keep Vr as it was...Or, better yet, it would be better to increase it...
Again, it's a tradeoff...You're sacrificing a small bit of performance (or safety margin) on one end, to give a bit more safety margin on the other.
So, the crux of your question is: So, we reduce V1 because of the tailwind...but why not keep Vr as it was?
Again, it's an issue of climb gradient...what is the minimum required...what you'll actually have under your specific set of circumstances...
Consider this:
Why not reduce the V1 by a bit due to the tailwind (as discussed)...but INCREASE the Vr to that above what would be for Zero wind? Okay, now you're accelerating from V1 thru Vr on one engine...going very fast down the runway...even faster due to the tailwind...so, all is fine...you rotate at Vr, but you're running out of runway because you've rotated later...while going very fast (due, in part, to the tailwind)...running out of runway...and, you've got a FIRST-SEGMENT requirement. Uh oh!!!!!
Or, what about tire speeds????
Again, it's all in the tradeoffs. You can do all kinds of adjusting...here and there... Ultimately, you can reduce your actual takeoff weight.
In the end, the charts are true and correct. The figures in these charts take into account (I hope) all these factors. :> :> :> :>
Tom