Perhaps legacy software is becoming the problem. In any system there's bound to be a dependency or any kind of use of a legacy piece of software with known bugs/exploits. Hackers identify these weakest links/weak spots and use these 0-days as entry points to breach the system further. As more systems are developed, it takes so much more time to track these weak spots, let alone maintain them.

So I think you're right. It's a miracle that the Internet even works. At all.