I have a sneaking suspicion that Dell probably had standing orders to not bother to argue with someone who wanted a reimbursement for Windows, and just get it over with. If you care enough to want that, you care enough to argue your case and make life a hassle for everyone if Dell refuses. To even ask the question is a shibboleth that instantly marks you as someone on the edge of the bell curve.
I also have a similar suspicion that that order has been lost to time, partly because it's very rare that people do that (and Dell even offers Linux machines to those who do care), partly because the support's been outsourced to someone who hasn't read that part of the script, and partly because the world has become more hostile towards consumers during the past 15 years.
It's been very funny to go through life discovering such shibboleths exist in so many random places and its like getting a powerup to even find out about them...
It took some court cases to get there...
Tbh I worked in customer service for a long time and almost always we would give a refund for whatever the customers asked except in rare cases.
And exactly like you said if the customer cares enough to reach out, just give them what they want. Best case they are super happy and recommend you and if you don’t comply they might go ballistic and do all kinds of stuff that will damage the business way beyond what the refund costs (very little)