Not really, Ruby has plenty of curly brackets, e.g. 5.times { puts "hello!" }.

In both cases, while it wasn't curly brackets that drove their adoption, it was unavoidable frameworks.

Most people only use Ruby when they have Rails projects, and what made Python originally interesting was Zope CMS.

And nowadays AI/ML frameworks, that are actually written in C, C++ and Fortran, making Python relevant because scientists decided on picking Python for their library bindings, it could have been Tcl just as well, as choices go.

So yeah, maybe not always curly brackets, but definitly something that makes it unavoidable, sadly Modula-2 lacked that, an OS vendor pushing it no matter what, FAANG style.

Which AI/ML frameworks are written in Fortran?

Probably none, it was more a kind of expression, given the tradition of "Python" libraries, that are actually bindings to C, C++, Fortran libraries.