I believe it's in The Dance doc that Rob Cavallo talks about the spark for doing The Dance came from him... He talks about how Lindsey had done a solo record and wanted to get himself back out as a solo artist. And Rob states that he said to Lindsey "You've been out of the industry's eye for a number of years now. You know what would get your name back out there in the biggest possible way? A reunion, on soundstage, filmed." I'm sure in those conversations the decision was made to not just film but professionally record it in the hopes of releasing an album from it, hence, they did. The same conversation would have been had in Stevie's camp, with her management reaching the same conclusion... she was not at the forefront of the industry anymore, tours not selling so much, etc. The Dance was a business decision for all of them far more than an artistic decision at that time (with the understanding that by getting lots of attention that would get them the industry support to then
afterwards go on to do other artistic things.)
The thing is that now Stevie sees herself totally differently. She said after the tour with the Pretenders that that tour "puts me in a different level as a solo performer". She wasn't second to Rod Stewart or whoever, SHE was the headliner and with the right opening act she realized she could now play the same big venues but WITHOUT Fleetwood Mac. Less hassle of compromising to other people's visions, no sharing of the profits, no compromising on tour schedules, being the BIG BOSS of everyone and everything... this boosted her confidence and she figures she fought long and hard for that and she is not giving that up for anyone or anything again...
She always talked about never leaving FM because loyalty blah blah blah but really she didn't ever leave them because it was her
safety net. She's come to realize at this point in her career, the tables have turned, and she does. not. need. them. SHE has become THEIR safety net now. She's got full control, not even Lindsey can touch her now, and she ain't giving up for nobody.
During The Dance, she needed THEM. Her career was stalled out. LB's solo career was stalled out. FM's career was stalled out. They all had motivat$on to get back together. This band has always been and will always be motivated by the moolah.... and for Stevie, the fame. She literally has given over her whole life to creating the legend of "Stevie Nicks" and she's finally gotten the payout for that she wanted. It's her validation that it was all worth it. She feels like she's swallowed enough sh^t and she's not swallowing any more.