The world has changed a lot, in terms of how things are used. A lot of tech nowadays has built in obsolescence. Meaning it has a lifespan and you kind of have to throw it away. In a world of yearly or bi-yearly updates to things like phones, or laptops... a great deal of things that use modern technology as we would think of it now... it's built to go wrong, to get you to get something new. And the speed at which things are advancing is faster now than it ever was. Something you bought three years ago will, in all likelihood be badly out of date if you compare it to what's around right now.
It's a sign of the times we live in. And people born in more recent times have grown up in that world. Because that's how it is. But that isn't how it always was. And I think your grandparents are basically a product of the times they lived in. Where manufacturers would pride themselves on something lasting twenty-five, or even fifty years. Where frugality was a buzzword and people were taught how to make the best of something, or make everyday objects into something else. I remember it as a kid in the 1980s, all the tips on how to turn washing up liquid bottles into pen holders, or make your own toys, and lord knows what else. The whole "make do and mend" mentality. It was big when I was a kid. And it's something that, as you point out, has been around since the end of WW2.
That isn't so much the case now. The world has changed. But people's attitudes can take an awful lot longer to change, if they ever do. More and more stuff is electronic based, rather than mechanical based. And with that comes a much faster rate of decay if you like. But it seems to me your grandparents still have that mindset. That's the world they grew up in, the world they were raised in.
The weird thing is, with many things there's a sort of grey area. It starts off new and desirable, then it goes into the "Omg why don't you dump that junk?" phase, and then a few years later it ascends into Antiquehood, where it suddenly becomes desirable again. Kitchen appliances from the 70s can be extremely expensive now, because they've crossed the threshold into Antiquehood. And are seen as the "in thing." At least in my corner of the world, lol.