The fundamental issue here is there was never any industry standardization for laptops like there was for desktop PCs. An ATX case (https://en.wikipedia.org/wiki/ATX) from 1995 can still be used as the enclosure for a 2018 desktop. That's 23 years. (See the "sleeper PC" subculture)

If a few component manufacturers came together and standardize component dimensions and tolerances based on something like an IBM ThinkPad, and an age of upgradeable laptops could have occurred.