We ask this rhetorically on many threads.
I suspect it is because boys see their surname as theirs, not their father's.
The whole 'women change surname when they create a new family with a man' sets up the subconcious feeling that her name pertains to the min man in her life and swaps from father to husband.
To compound this - many of the men women on MN report wanting to dissociate with are step fathers. Men whose mothers renamed themselves for. Thus compounding the sense and expectation that women re-label themselves according to the man in their lives
But for a boy / man, they feel their name is rightfully theirs, not temporary, not stuck on, not subject to any ifs or buts and not partly owned by anyone else, e.g father.
And a woman (or man) can change her name for any reason at any age over 16 (18?). She does not need to wait for man to marry her and save her from the name connection with an abusive man. But many women do - understandable because of the admin involved, but it's always there as an independent opportunity, man or no man.
All within the context that of course it is fine for individual women to change their name should they wish to. Do what suits you best and feel secure with that.
But I'm never sure why making that choice means you can't also critique the bigger picture in an objective way.