This is an interesting topic @Yuvraj_Wadhwani, most of our backlinks come from the gratitude of our fellow bloggers linking to our articles, our online interviews and other expert posts where we share our views on specific topics.
Apart from this, whenever we write any reviews (product, service, etc.), we'll try to message/email the brand and let them know about this. If our association with them is good, they'll respond back, and we'll request them to use our article as a resource on their website or their official blog press release. Most of them will feature our link in their testimonials and reviews section.