(Why) does Android connected to Mac not just behave as a normal USB drive? When I connect my Android (Galaxy S5) phone to a Windows computer, I can browse the phone storage just like any USB/external drive. That's not the case on Mac. There I need to install Android File Transfer or something, which seems to be unresponsive and slow.

Is there no way to just mount my phone like any other USB drive on Mac? If not, could you maybe give a short explanation, why?
The Default mode for Android USB Transfer is MTP (Media Transfer Protocol), which isn't supported by Mac.


  Apple’s Mac OS X is a holdout — it doesn’t include MTP support at all.
  Apple’s iPod, iPhone, and iPad use their own proprietary syncing
  protocol along with iTunes, so why would they want to support a
  competing protocol?
  
  Google provides an Android File Transfer application for Mac OS X.
  This application is just a simple MTP client, so it will work for
  transferring files back and forth on a Mac. Google doesn’t provide
  this application for other operating system because they include MTP
  support.
  
  Source: http://www.howtogeek.com/192732/android-usb-connections-explained-mtp-ptp-and-usb-mass-storage/


So, that's why you need an extra software for Mac, because Apple only wants its devices to be supported.

To avoid that, you could try to mount your SD Card in USB Mass Storage (UMS) Mode.
That could be easily be done from Settings if you're using Android JellyBean or below.

For KitKat (4.4) and above, you need to have a rooted device &amp; some other external apps like Universal MASS STORAGE Enabler (created by me) or USBSharer or whatever.