We don't wander around the sky for the hell of it, we just let the plane follow the magenta line.
This maybe the case with yourself and at your airline. Is this the case with every single aircraft in the sky? Definitely not. Hence why headings are used.
Towards the end of the year the UK will get its first PRNAV1 routes which will allow for routes to be put closer together and lessen the use of headings between aircraft which are suitably equipped. However, although this will reduce the use of headings a bit, expect the use of headings within the UK for a long time to come yet.