The B-52s are like Trigger's broom - constantly repaired with parts and wing skins replaced. Whilst from what I have read some parts of the B-1are either impossible or prohibitively expensive to replace.
Plus it spent a lot of time in a high stress low=level role - and strangely spending a long term loitering at high level with the wings swept forward - for which it was not designed, as proved as punishing.
https://www.airforcemag.com/b-1s-can...along-the-way/
https://www.thedrive.com/the-war-zon...-to-this-point