Right, web apps aren't websites. The distinction is pretty sharp when you move from a simple static old fashioned display to Amazon tier complexity where money is being transacted, log in information stored, orders updated, and a million more things besides.
The big question is if the internet and its primary portals, the desktop browser and the smartphone, will reach the end of their tether. The only thing I could see replacing it is neurotechnology of some sort, and that seems so far off and so difficult to commercialize that it's not something web developers need to worry about any time soon. Or perhaps quantum computing becomes commercially viable and simply shoves digital computing aside, negating the need for those skills completely.
Another alternative is that the web radically changes unforeseeably and new practices instantly antiquate everything people are learning now, which is a more frustrating and realistic possibility and also something that is bound to happen. Given how difficult it can be for many people to learn these skills, and given how much knowledge one must integrate to be a productive developer, this is an upsetting potentiality and one that is bound to happen eventually.
Not every field carries these risks. Law practice isn't going to change fundamentally in the coming decades. And some aspects of coding can be exhausting and demoralizing to learn. Past generations of coders have had their skill sets rendered null and void and it will probably happen again at some point to this generation.