To put forward the opposite point of view...
Part of the joy of doing the BG (for me anyway) is the memory of the friends who shared the day. Despite it being 20 years ago I distinctly remember the moments with each of the friends who ran alongside me when I did it (despite having an appalling memory for almost everything else in my life!!)
And conversely I have always always enjoyed running alongside others when I've supported other rounds - new or old friends.
Going solo, OK you have your own memories but you don't have those shared-experience memories.