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
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
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 & some other external apps like Universal MASS STORAGE Enabler (created by me) or USBSharer or whatever.