https://stanfordmag.org/contents/shower-or-bath-essential-an...
My first home, a two up, two down terrace - guessing around 500-700 sq feet, it was tiny - had a bath, partly as I would not have bought anything without. There's not much in the UK without anyway. I've always liked shower for mornings and refreshing, bath for unwinding and relieving aching muscles with a long soak, so if limited space shower over the bath would be our compromise.
Was much easier - and probably much cheaper - with the kids, as they reused the water, or shared when younger, and mum or I could go in last - assuming they hadn't come in caked in mud. :)
In this case, shower can be converted back to the bathtub, for not too much money/time.
Besides, once the house is sold, usually some interior changes are made by seller and/or buyer, e.g. new paint inside, new appliances, furniture etc, which all takes time and money and converting the shower would be just one more thing to do, and a relatively cheap one, too.
Yes, you can put one in for not a massive amount of money, but that's money that the buyer will want to knock off, or they'll just go for the myriad of other houses that DO have a bath.