As per the Moz
Further they also stated that
They also clarified that it is not a calculation of spam score of sites linking to your site so they don't consider spam score of backlinks while calculating your site.
Also If you check their
27 common features it includes low numbers of pages, length of domain, title tag, description, Meta keywords, links to linkedin, canonical, favicon icon, Facebook pixel, google tag manager code and many things that many of the sites lack and hence the sites are having high spam score due to that.
Thank you, till now I never taken spam score seriously but after reading their criteria for calculating spam score I think I am going to avoid DA, PA to as these metrics can be easily manipulated these days.
Coming to your question if you read their
27 common features then you will come to know what needs to be changed to reduce the spam score
. You will get your answer if you compare site with 50% spam score with same site when the spam score is reduce, you will get the idea what considered by Moz to determine spam score.
People just see the spam score is high and they run to check for shady linkbacks but Moz never told that spam score is depends on shady backlinks.
Reference:
Code:
https://moz.com/help/link-explorer/link-building/spam-score
Even google has 28% spam score

(Just checked out of curiosity

)