Yes, because they try to strip the binaries as much as possible so that the file size is smaller. If you compile a regular "hello_world.c" with gcc -O3, the size is 8 kb. You can def make a malware that is way smaller that does something simple like change some registry value to some uri.

Average size for malware is ~100kb-200kb btw. This is way smaller than almost any software besides some console games.