Why would people do this?

I'm not a rabid feminist, but if a potential spouses surname was Pratt, Allcock or Longbottom I'd be keeping my name.

And if the name was Smith, what then Miss A

Smith would be fine.
I might tag it onto my name, which is much more grand.

I'm not the poster who mentioned the "s". Dear God no I'm not
However.
I think the meaning is that women who become Mrs John Smith upon marriage are in fact now MR John Smith with an added "s".

Their whole identity is now his name, apart from the "s" that makes Mr into Mrs.
Hence we are "just an s".

Hmmmm.

Isn’t Mrs a corruption of Mistress?

Yes, but Mistress didn't have the connotations it has for us nowadays. A household was headed by a Master and Mistress, abbreviated to Mr & Mrs. the abbreviation became the titles, hence the strange spelling.

Iam64
I wouldn't jump to conclusions if I were you.
'I think we all know what you mean'
You may 'think' but you don't *know. I *believe in both pronouncements.
Feminists are often in your face with their protests and raucous to boot and, of course, anyone can choose to be known by most names. There are, as we have seen in today's news, some unacceptable exceptions.
It doesn't 'do'for you to act as the mouthpiece for everyone who posts on GN.

Gabriella you live a sheltered life if you think it is 'rabid' not to use your spouse's name!
I agree it is courteous to use the name an individual chooses to be known by. Seems odd to stop calling a woman Mrs Smith just because Mr Smith died!

PECS
I did say that, of course, anyone can choose to be known by any name, did you read that part?
I myself have reverted to my maiden name as I am divorced but others do what's right for them.
I stand by my remark about rabid feminists. Note the word 'rabid'. Feminists who don't push their views in your face are not rabid.
I'm not in favour of placard waving protesters of any persuasion and, for feminists to try to say that men and women are equal on all levels is like saying that chalk is the equal of cheese. Both have their strengths but not all those strengths are equal...IMO, of course.

No Gabriella what you said was

"It's only rabid feminists who insist on keeping their maiden name."

You did not mention placards or 'in your face' ! I am someone who has marched often, with a placard, to express my opinions and exercise my democratic right to peaceful protest. Assume then you think I am rabid! However, just my northern working class roots coming out

Yes, I did, but I should, maybe, have highlighted the word 'insist' as the rabid minority of feminists are very very vocal about keeping their 'identity' et al, which is in stark contrast to those feminists who go quietly about their business. There is no need to loudly proclaim your 'rights'.
I know I did not mention placard waving in my post but that does not mean that I can't add it to any subsequent comment.
I am originally from Liverpool and working class but a peaceable person. There are all sorts of stones in the same stream.

Often there is a need to proclaim your rights loudly, otherwise you don't get any.

Having a really bad day with tchnology and most other things. I was probably fiddling with the computer settings.

Here goes ?

Can't write either.

gabriella I am peaceable too! But I can still wave an anti-war placard.

Anyone can do anything including placard waving, and each suffers the consequences of their actions and inactions.
I reserve the right to my opinions and the right for you to hold yours.
Yours are no more valid than mine, and vice versa.
GN is a useful site to share, offer and discuss, agree and disagree, sympathise and criticise and each of us 'talks' in our own way, which is good, as long as we don't single out individual members to be the butt of jibes or 'gang up' on someone who posts a different view.
IMO, raising one's voice in order to be noticed (as advocated in one post) is not a good idea, nor is placard waving but I repeat, it's entirely up to the individual.
My ways are not your ways and, if we all agreed on every subject, we'd have nothing to discuss.

Gabriella of course we are all entitled to act as we please within the law.
What I was suggesting is that it is not 'rabid' simply because it is not the way you choose to be!