the answer is pretty easy: macos is based on bsd is based on unix. from a security pov so far it won't get better. user accounts and system wide access is pretty limited, so if you for some reason install a virus on your user account, it wouldn't be able to get completly under the hood, unless it expolits an unpatched weakness. windows has a ton of legacy code from the 9x days and early nt still being baked into the system, preventing microsoft to do a proper redesign of windows because it would break legacy support. microsoft also has to allow much more "wild" software to run on system level, like esoteric drivers for obscure hardware, opening the doors wide for hostile software.