Padme fakes her death, takes Luke to Tatooine with Ben to arrange things with Owen and Beru, goes with Bail to Alderaan to raise Leia, assumes new identity, dies of natural causes, (or an accident) while Leia is still a toddler. Problem solved.
That would take too much screen time after the climax. That would take a whole other movie. Also, why would she leave Luke with Owen and Beru if she was still alive. Why wouldn’t she want to raise both of her children herself?
It could have been assumed, especially since Leia says that her mother died when she was young. That’s the problem with the prequels. Everything had to be tied into a neat bow. Why couldn’t we just be left to assume that Boba Fett was some bounty hunter trying to make his way in the universe? Instead, George had to spell it out that he was a clone from New Zealand.
Personally, I like for all loose ends to be tied up in a story.
It isn’t a “loose end” to not know how Padme died. We know from Return of the Jedi that she died when Leia was very young. To see her die is unnecessary. A loose end would be if nowhere in the OT was Padme mentioned, and she just vanished in between the two movies. It also isn’t a loose end to not know who Boba Fett was as a small child. It is irrelevant information inconsequential to everything in the story.