Since this gets to why the heck my partner and I would be teaching flourishes every week, I think it's relevant to this blog, so I'll speak for myself here (and I won't presume to speak for anyone else, not even Steve):
For me, contra dance lets me enjoy music without having to be crazily self-conscious as I would find myself in a club, or a more free-form partner-oriented dance genre (or a more closed-off social scene), and I don't have to worry about it. The choreography is there and taught right before (and during) when I have to do it to stay with the group, and everyone else is doing more or less the same thing at the same time (so at least if I look like a goof, it's likely others do too, and that makes it okay). I can dance contra straight up, as written, with various different people through an evening, and I have a wonderful time.
On the other hand, if I have a bit of extra energy and a willing partner (or neighbor), we can do the dramatic dips or the dizzying twirls -- and as long as we're back where we need to be when we need to be there, we can pop back in and dance with the other folks in our set, regardless of whether they decided to embellish the dance on the previous move or not. And I also have a wonderful, albeit differently-energized, time.
But if for whatever reason I decide that I'm not up for flourishing, there's still a rewarding experience waiting for me in the choreography as written. That baseline does't exist as much (at all?) in other scenes.
I adore that flexibility and the ability to dance with the group, too, even if I take a moment (or phrase) just with my partner. That doesn't exist as much in other dance genres and venues, and while I may love the occasional dramatic dip in the space of a swing (assuming the room's not crowded) and share that connection with my partner, I also really like that I can pop back up from it and flow into a star with my neighbors and share that connection with them, right on time.*
That's why I do it, anyway. I know there are lots of other reasons. Flourishers, what are yours?
* After the fact, it occurs to me that this is related to why I like changing up the music from time to time, too. Being able to enjoy the music with familiar choreography as a touchstone and a relatively safe (and intergenerational, at least in my community!) environment has a lot of appeal.