I could be utterly wrong, but I suspect part of this is that applying for jobs has become so quick and easy - a button click - that entities advertising jobs are utterly swamped with utterly worthless applications. It's a bit like email spam - I remember back in about 2000 and something, before I sorted out my own email, getting literally ten thousand plus spam emails per day. Imagine the same, but it's CVs, and some…
But I think that's probably a different problem. If we exclude the clueless applicants: the hiring pool is just so much larger. Back in the day you'd live in city X and you'd get get a job in city X, or maybe neighbouring city Y. The number of devs in that location was often in the thousands, or maybe even hundreds (depending on size of city X and Y, obviously).
But now it's everybody in the US, or everybody in the EU and Africa, or everybody in the world.
"Get the best applicant out of five qualified candidates" is one thing. "Get the best applicant out of five hundred qualified candidates" is quite another.