The amount of days is not random.
All these abusers always pretend to be innocent exploiting the fact majority of users do not dig deeper and are clueless about the reasons for blacklist.

The appeal period is proportional to the amount of abuse, recidivism, time spent on Steemit and reputation gained while abusing. Flysky has received multiple warnings since 2018 to stop photography and art plagiarism before but refused to stop.
His long time spent being active on Steemit (2 years) means that he must have learnt what is frowned upon by the community and counts as abuse. This means that his activity has been intentional.

He has been caught for photo/art plagiarism 7 times. 6 times for tag abuse/spam.
These are just few occasions he got reported for. It does not mean that these are the only ones.

His whole activity is filled with spam such as comment spam and spamming by repeating the same content multiple of times throughout the year. He has done it on at least 3 other accounts (all blacklisted).