Bingo.
They are showing empathy because smart, sensitive people know how frustrating it is to lose a point like that.
Let's be honest. It's sad that you haven't come across decent, good sportsmanship players that prefer to win by their merits. You assume everyone is happy and enjoy to simply win like you. Especially this is all recreational.
Let's extend the scenario of your win/happy idea. Are you happy to win a local tournament that you paid good money for if the opponent rolls his ankle after 2 games and retires? Hey you still get a win. How about in a lesser extent, your opponent just got fired from his job and terribly distracted and couldn't play well at all?? Score is 6-0, 6-1 in your favor after 70 minutes.
I know I definitely won't like it one bit.
There are ways to acknowledge a bit of fortune. Saying sorry is not it. Its disingenuous. You're not sorry at all. The operative is the word sorry not the acknowledgement.
Saying sorry is more likely to rub salt into the wound of your opponent.
You know the scenario as we all do, its a long hard point, maybe at a crucial time, it clips the net, you win the point, you're kind of smirking and glad inside but you say sorry when you don't mean it
You know it, you're opponent knows it, everyone watching knows it.
You wouldn't say sorry if the ball catches the line. That's good fortune too. When we see hawkeye and a ball catch the corner by 1mm we all laugh and smile we dont say sorry.
In fact next time you serve an ace that barely catches the line, say sorry as a measure of "sportsmanship". Are you actually sorry? Do you think you're opponent thinks you mean it? If people started saying sorry in these instances as well as a show of sportsmanship it would be irritating.
BTW if smart, sensitive, decent, people (Which I assume youre trying to refer to yourself. Thats nice.) like to win on their merits, do you offer to replay the point, or lets say in fairness, especially if you have formal rules, give them the next point for free to equalise things back again? Or do you just take the point. Talk can be cheap about self virtue.