If it would be strange for a child to know their biological mother was dead, you don't think it'd be strange for them to know that they grew in a dead woman's uterus?
"If a young woman loses her life it can feel like her life was in vain, wasted because she lost it when she was young."
But it's okay if another woman can use her uterus to make a child? She's served her purpose after all, and so it's okay that she's dead? I'm sure that's not what you mean, but that's how it sounds.
And the issue is that some families might get peace of mind that their female relative didn't die in vain (although that's a rather silly sentiment). The family. Because as uterus donation is not something listed, and I imagine not something that people consider being incredibly rare, I very much doubt that women who die in rare enough circumstances that their organs can be donated, will have had a conversation with their female family member about whether she would want her uterus donated.
There is no explicit, clear consent from the pertinent party, only a family guessing what she wanted, with their own agendas at play. That's not good enough. It would be very easy for the NHS to add the uterus and every other specific organ to the list of possible donations. So why don't they?