It's definitely not impossible to prevent issues like this, it just requires effort.
Securing a network/host/application is like getting (and staying) in shape. It's a process that requires an ongoing effort. There's nothing you can buy that will take care of it forever.
Most breaches aren't the result of "impossible to prevent" attacks, they're the result of basic due diligence not being followed. You're right though, that it seems some days like that's the rule and not the exception.
While you can't have an "unhackable" site (or an "uncrackable" safe), it's all a matter of risk vs. reward. You can certainly ensure that your site doesn't have any vulnerabilities listed in the OWASP Top 10 (and test it repeatedly over time to make sure it stays that way).
And that's not even getting into a more mature vulnerability management process that involves outside assessments, source code reviews, and threat modeling. All those things are also nice to haves (or may be required, depending on your industry and the type of data you have access to).
It's totally understandable to be a pessimist about the state of security in our industry, but preventing these types of issues is not a Sisyphean task.
