Yeah, of course they did it to sell more phones. Phone OEMs sell more units when the units are as compact and water/dust proof as possible. Sealing phones with adhesive maximizes both of those metrics, with virtually no (non-hypothetical) trade-off to the vast majority of users.

Maximizing profits by maximizing the characteristics of smartphones that customers care about is not only a perfect explanation for sealed internals, but it’s the only explanation that stands up to any amount of critical thinking.

The “they want to force you to upgrade” narrative is popular because people want to believe it. I mean, obviously they want you to upgrade, but they also know that consumers are more likely to buy their products over competitors’ if the product has a reputation for longevity. Which is why OEMs like Apple support their devices for as long as they do, and even tailor software to provide a consistent experience with a degraded battery. If they wanted to plan for there devices to become unusable after a certain time, it would be a lot more straightforward for them to just stop doing the things they’re doing to make sure devices are usable for 5+ years.