Why are the offenses against Blessed Virgin Mary are called blasphemies instead of sin? There are five types of offenses and blasphemies committed against the Immaculate Heart of Mary:
  
  
  Blasphemies against the Immaculate Conception. 
  Blasphemies against Her Perpetual Virginity. 
  Blasphemies against Her Divine Maternity, in refusing at the same time to recognize Her as the Mother of men. 
  The blasphemies of those who publicly seek to sow in the hearts of children indifference or scorn, or even hatred of this Immaculate Mother. 
  The offenses of those who outrage Her directly in Her holy images.
  


Top 5 Sins Against the Immaculate Heart of Mary

Why are the offenses against Blessed Virgin Mary are called blasphemies instead of sin?

Looking for Catholic Foundational Teaching and explanation on blasphemies against the Blessed Virgin Mary.
Because blasphemy can relate to that which is very sacred to God also, as it is written:


  Revelation 13:6 (DRB) And he opened his mouth unto blasphemies against God, to blaspheme his name, and his tabernacle, and them that dwell in heaven.


Cf. Jude 1:8, 10.