I can't speak for everyone, but I'll give the "why" a try.

1- These guns are simple, no safeties to mess with
2- These guns are flat sided, no safeties to mess up the clean lines
3- Trigger pulls are consistent shot to shot
4- Some of us don't like using SA for defense guns, too easy to make a lot of noise when you aren't ready
5- Many of us, who learned early on to shoot a revolver properly (double action), find the transition to a DAO auto (not the Glock safe action variety, which I have trouble equating to DAO) simple and easy
And, with the S&W original Third Gen DAO design, the trigger pull is about 2/3's the overall travel compared to the first shot of a TDA gun, so, it's less hard to have an accidental discharge as in a SA gun, yet still provides the DA trigger stroke dynamics like a revolver, just a tad shorter travel overall.

Or, I could just say something along the lines of the bumper stickers I see on the back of Jeeps.... "It's a Jeep thing, you wouldn't understand.."

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.............SmithNut