There's a lot of variation. Materials change. Stuff wears out. I have old gear and I have gear I've replaced because what I wanted wasn't available 10 years ago.
As for boot. I have custom boot that I've had for a couple decades (and have had repaired). But they're heavy and I don't wear them for everything.
We probably shouldn't take "for life" any more literally than we do the "four hour workweek". It represents an idea. You might not want your boots to last forever and may in fact decide to replace them after 6 years. But if they were sufficiently well made, then you'll get more for them when you sell them and they'll last longer for the next owner if you sell or donate them.
There's a lot of variation. Materials change. Stuff wears out. I have old gear and I have gear I've replaced because what I wanted wasn't available 10 years ago.
As for boot. I have custom boot that I've had for a couple decades (and have had repaired). But they're heavy and I don't wear them for everything.