And, they are both very tightly integrated with Sage via C library interfaces (between Python and Pari/GAP), which took many years of pain to properly write and

And, they are both very tightly integrated with Sage via C library interfaces (between Python and Pari/GAP), which took many years of pain to properly write and debug. I wrote the first versions of these interfaces, and Jereon Demeyer and Nils Bruin massively improved and rewrote them over the years. Much core functionality in Sage fundamentally relies on Pari and GAP in order to work efficiently.