People have limitations

We, humans, crave pleasure and positive emotions and avoid things that make us bored or uneasy. Having a long registration page with too many inputs is the best way to make sure users never finish the signup flow. 

So how do we avoid this?

• Practice progressive disclosure. Avoid "serving" big chunks of content at once. Instead, reveal information step by step and move from simple actions to more complex ones. For example, you can divide forms into steps and heavy content into digestible blocks. The goal is to provide only the information users need at any particular moment.
• Use headlines for structure and capturing attention. Headings help you kill two birds with one stone. First, they generally increase legibility and scannability. Second, a clear heading hierarchy is crucial for users with visual and cognitive disabilities.