The same mentality is widespread in photography, heavier metal construction (even though often just exterior shell and interior is polycarbonate) and weight are associated with quality and longevity. But it's starting to change as more lenses are exclusively made from "engineered plastics" - a marketing term to make these new lenses sound better.
OTOH, those robust lenses from the 50s to early 80s survived until today and are often still used and adapted on modern mirrorless cameras.
Oddly, for a camera, I prefer some weight. Not so much I will get fatigued, but it is easier to hold steady if it is not feather weight. And having it balance away from the lens is nice.
The oldest lenses I have that I still sometimes use are from the late 1940s, though they are both large-format lenses in shutters (that have been serviced). The main issue with those is that parts are scarce.
I wouldn't expect any gear made today to have that much of a lifetime.
Eh, I would. I recently repaired an old Tamron 28-75 2.8 for Canon EF, as well as a more modern Sony SEL2870, and both were pretty simple. In one, the autofocus and aperture were done by bog standard 4 wire 8 ohm stepper motors, with standard four wires rotational encoders, and in the other it was another standard three phase brushless motor, four wires for the IS electromagnets, and optical encoders for the rest.
That is to say, the electronics are fairly standard. You could easily make a single board that can drive the electronics of pretty much every lens. Projects exist going in that direction.
As for the construction, it's pretty damn solid. It's not fully metal, by very high glass fiber percentage nylon and polycarbonate. Very, very durable materials, in some cases even more than metal.
And because of advances in manufacturing tech and the fact these are made of multiple simple plastic parts, you can fabricate replacement parts fairly easily.
Given the fact that the Tamron lens lasted 15 years with the only issue being the aperture cable getting damaged and two pins getting bent out of shape, and that even the cheapest modern lens was fabricated similarly, I think it's not unreasonable to think they could last 40+ years given sufficient effort. Certainly for the most worthwhile lenses.
Of course, when parts need to be made out of metal for mechanical reasons, they often still are. For example, mounts, threaded rings, and so on.
At least this mentality is rooted in reality, as we now have a pretty good data on longevity of plastic cameras from the 80s and 90s that routinely outlast their metal+leather counterparts from the 60s. Here's a very typical "plastic in cameras" horror story:
Another simple example. I bought a zojirushi water bottle 5 years ago, it is still going strong, still keeps water cold for a hours and hours. I bought another bottle 3 months ago, which is much heavier/sturdier than zojirushi. It sucks (it is so strong that it can be used as a weapon though).
The plastics chosen for lenses are incredibly resistant to UV light due to many additives and often powder coatings, and in general incredibly dimensionally stable. This is actually when even very expensive lenses often use plastics inside, because those plastics don't expand/contract/deform as much because of heat as metals, leading to more precise optical alignments and higher image quality.
Ironically, since these lenses often need much smaller adjustments and don't need as much to be readjusted after taking them apart, I find it easier to repair them than some complex metal lenses.
OTOH, those robust lenses from the 50s to early 80s survived until today and are often still used and adapted on modern mirrorless cameras.