What, if anything, am I missing here?

Not caffeine obviously. When you normally drink decoffeenated, a weak coffee suffices. And anyway the world wants excesses of caffeine so a weak coffee is still overstocked with caffeine. They even put it in shampoo fer gawds sake!

Instant is instant. If you want to re-hydrate and want something different from water.

Personally I switched from regular instant to decaff because I was getting what I described as "long QT" whilst trying to get to sleep. A sure sign that at my modest level of caffeine input it was affecting my heart in an abnormal way. But experience showed I would get a headache by 11am so I have regular Kenco Smooth first thing. And no headaches. But now if I pick the wrong jar & don't get caffeine it doesn't cause headaches anyway. Job done.

Caffeine is a drug and it is physically addictive. Try going without coffee (or tea) for a day. But keep the asp(i)rins handy.

FWIW Tea has twice as much caffeine as instant coffee, and filter/cafetiere has 5 times as much as instant. Hence the myth of tea v coffee - you can see where it came from.

On a really sad note, I was bragging that Stroud has no Stirbacks, but my town (5 miles away but near the Motorway) has an ex HappyEater/ex Little Chef which is now........ AH! I can bring myself to say it.