The bigger the product, the bigger the target. Wordpress is a target because it is so popular. Same reason Windows has always been a major target. To their credit, they patch quickly when something is found. Wordpress hacks are low-knowledge low-skill attacks - attackers have their botnet run a script they got somewhere.
Update promptly, don't take defaults in your configuration ( don't ever use "admin" for your admin user!!), install and use one of the WP security plugins (most of them do some type of IDS and can alert if a core WP file is changed), hide/rename wp-login, limit login attempts, set strong passwords...
I hate sliders to begin with (they're evil from a conversion standpoint), so that specific threat missed me. I also don't use dodgy random themes.
Once you get the malware off your site Google should reinstate. As long as it doesn't happen so often that you get a "history,"