Off-page SEO is like the work done backstage, if you will. It's the work that isn't visible to readers, but it's just as crucial as On-Page SEO in getting your content noticed and gathering responses.
Let's use an example to make it clearer why in the SEO checklist Off-page SEO is important. If a builder constructs a home, obviously the outward appearance matters. However, if the foundation, cement, and bricks aren't properly taken care of, the house will eventually collapse. Here, the importance of both the outward look and behind-the-scenes work is equally vital. The same principle applies to SEO. If Off-Page work isn't properly managed, it could negatively impact Google's rankings.