We do not list cmake as a requirement for the ET but some ExternalLibarries require it. A quick use of grep reveals:

grep -li cmake arrangements/ExternalLibraries/*/src/build.sh

these

arrangements/ExternalLibraries/ADIOS2/src/build.sh
arrangements/ExternalLibraries/AMReX/src/build.sh
arrangements/ExternalLibraries/NSIMD/src/build.sh
arrangements/ExternalLibraries/openPMD/src/build.sh
arrangements/ExternalLibraries/yaml_cpp/src/build.sh

For some cluster we may be able to enable cmake using machine.ini settings by loading a module, but for generic.iniwe either have to declare cmake a ET dependency and then provide instructions on how to install it on the supported Linux / macOS hosts or disable the ExternalLibraries (and their dependents, ie CarpetX) by default.

--
Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2761/some-externallibraries-require-cmake-to