I understand that your goal is to enhance SEO. I can recommend https://crowdlinks.store/en/
a store where I recently purchased crowd links. The quality was decent, and I noticed an increase in traffic. They offer various packages, so you can choose one that fits your budget and needs. My experience with them has been positive!
Regarding why crowd links work, it's related to increasing the authority of your website and improving its positions in search engines. The key is not to overdo it and to remember the importance of quality content on your site. Good luck!