Making components replaceable increases volume, weight, and cost.
If you want replaceable components, go buy a computer for which that is a feature - and know that you will get a machine which is larger, heavier, and more expensive (all other factors being equal). Swapable components require additional casing, connectors, testing, sales channels, etc. You're not going to get a 3/4" 5-lb 7-hour 256GB-SSD 8GB-RAM MBA Retina for $2200 and be able to swap out darn near everything; something's gonna give.
Some of us DON'T want to replace components, having learned over the years that by the time we're replacing components we'd rather replace the whole computer outright. If I need more RAM, it's best matched with a new CPU. If I need more storage, I'll need more RAM to throw around more data. When the battery dies, all those other components are gettin' obsolete anyway. I also know from experience that upgrading parts doesn't always go as planned, and time wasted upgrading can very quickly add up to the cost of a new machine outright. I'd rather have a notebook which is very thin, very light, very fast - and just replace the whole package when the time comes as I see fit.
You're welcome to a different POV, and there is a market happy to serve our different needs & desires.
However, just because we have a different POV doesn't make me a f*ing idiot.