I'm confused!

What I'm confused about is why plants appear to have so many names.   I've been given 2 different names now for these beautiful flowers that we have,   and I've googled both,  and they have the same flowers as we've got.  They are obviously both correct but why?  Why are they both called an African Daisy (amongst lots of other names such as a Cape Daisy)  but have different Latin names. 

Arctotis Stoechadifolia 
or

Osteospermum

If you look at  these links then you get  lovely pictures of our Daisies. 

So African daisy it is.