Link building will always be necessary, but how you approach it now is different from how people did it 10 years ago. Today's biggest challenge for businesses is how to find customers and sell. Search engine optimization plays a key role in this.
Social media has become a key tool for businesses. Content marketing strategies have also become very important. Google penalizes sites with too many backlinks to them. This makes it appear that link building is less effective than it was once. This is understandable since linking to too many other sites will likely mean that there isn't much original content on your site.
All these factors mean that link building isn't nearly as valuable for ranking your website as it once was.