Because only one in a hundred postings is real, we have to send out hundreds of applications before even getting a rejection. There's no way to tell if a posting is real or if anyone will ever read your application, so the only option available is to apply to everything.
A lot of people pose this as a prisoner's dilemma, but it really is not. This problem is not mutual, it's entirely one sided. If companies would only post jobs they intended to hire for, there would be exponentially fewer spam applications. They've fucked around by posting spam and now they're finding out by receiving even more spam.
When the average applicant has to send literally hundreds of applications to get any response at all, absolutely nobody is going to handcraft a thought out application to any one posting. There's literally not enough hours in the day. Because we don't even get rejection letters back, the only way forward is to firehose as many applications as possible and just hope you win the lottery by getting your resume in front of a human.
It's absolutely terrible for everyone involved and the only ones who can stop it want to act victimized by the problem they created