Why do people do spammy link building?
Spammy link building is one of the common negative SEO tactics. Instead of attempting to boost a site, the aim of negative SEO is to damage the rankings of a competing site, or even have it completely removed from search.
What can you to protect yourself from spammy link building?
If you think the links are hurting (or will hurt) your search engine rankings because of negative SEO, there are 2 things you can do:
First, you can quickly and effectively disavow them using Monitor Backlinks. Check out this article on how you can do it: https://help.monitorbacklinks.com/en/articles/924723-how-do-i-disavow-backlinks-using-monitor-backlinks
Second, you can also use the negative SEO protection, a free badge on your site that discourages people from launching a negative SEO attack on your site. It discourages them because they know it will be ineffective since:
a) they know you're using Monitor Backlinks to get notifications
b) they see that you have many referring domains.
If you want to add it, you can find out how to do it by following this link: https://monitorbacklinks.com/negative-seo-protected