Both decisions to use parentheses for both arrays and argument lists and omitting parentheses for call with arguments come from Ada's design goals of supporting programming at large. While this is contrary to some other languages that focus on specifics of implementation, the decision isolated design intent from implementation details.
The original "Rationale for the Ada programming language" book provides a lengthier discussion on these points.
TLDR; The syntax is an intentional language design choice which puts capture of design intent in the forefront over implementation details.
The original "Rationale for the Ada programming language" book provides a lengthier discussion on these points.
TLDR; The syntax is an intentional language design choice which puts capture of design intent in the forefront over implementation details.