Consider this: The smartphone in your pocket is 10 times more powerful than the fastest multi-million dollar supercomputers of just 20 years ago. There are tens of millions of lines of software in that phone of yours. There are hundreds of apps written by more than one million developers, some of whom are hackers, and some of whom are just incompetent at security. And then there are chips in your phone that run sophisticated software, from companies located in countries all around the world, all of which have security bugs.
The complexity is mind-boggling — and so are all the security vulnerabilities that exist and will be found in the future.