That's not new ("nowadays"). In general, today's vehicles give much longer, much less troublesome service than yesterday's did. Some parts don't hold up as well as they used to, and headlamps are an example. Yesterday's headlights were much more durable than today's because yesterday the choice was either massively over-engineered headlamps or no headlamps at all. Glass and metal were the only materials available. Mass was of zero concern, and neither was packaging space, which was a moot point anyhow because headlamp size, shape, and fitment was standardized by law.The overarching problem with automotive design nowadays is the expectation that people will trade their cars instead of running them into the ground
Are you old enough to remember what real planned obsolescence looked like? Now that was an ugly, greedy scam to get people to buy cars more often. Today's version looks like child's play by comparison to how bad it used to be. We all have fond memories of the old 1965 Whatevercar that ran forever...sure, with trips to the service station (remember those?) every 3,000 miles, and with a new look every dang model year nothing was ever put together properly. Remember those long lists of "sample defects" Consumer Reports used to list on the cars they tested? They don't have those any more because today's cars generally aren't defective like yesterday's were, right off the showroom floor.It's just a scam to get people to buy cars more often
I don't disagree with you that headlamp durability standards aren't sufficient, but that right there is the reason why headlamps don't hold up. Not because automakers think someone's going to trade in the car because of clouded headlamps, and not because automakers think the owner's going to install aftermarket headlamps.
Unfortunately, we live in a throwaway society. Heavy-duty cars that didn't change with every model year have been tried (Checker) and mostly they were a sales disaster. The Volvo 240 comes to mind, too; it is much prized for its durability, but it never sold in anything like the volumes of the more "conventional" cars with their frequent model changes and so on -- and the 240's durability makes it particularly ironic that 1986 and later models were equipped with very quick-to-degrade plastic headlamps!