Currently, the named_install step is defined as:

const named_install = b.step(b.fmt("{s}_install", .{key}), b.fmt("Install {s} to zig-cache/bin", .{ex.main_file}));

However the executable, by default, is installed in zig-out/bin, not zig-cache/bin.
Moreover, the user can change the destination, with the -p --prefix or --prefix-exe-dir options.

I will fix it.

By the way: is it really necessary to add an install step?