Why Scrum is most popular?

SCRUM is not a new framework. It is a time tested Agile framework, developed by Ken Schwaber & Jeff Sutherland in the year 1990

SCRUM is domain independent where as almost all other models are designed for technology projects 

Can be used for projects of all sizes and complexities 

SCRUM is easy to understand 

Most of the SCRUM knowledge is available in the public domain  (Scrum Guide)