It may have been a combination of things when you get right down to it.
As has been mentioned, the women's division in WWE is an actual division with talented female wrestlers now. They're not just there for eye candy anymore and have finally been a relevant part of the product for the past few years; as a result, there are women on the roster that fans are gonna be invested in and Paige has been one of them.
I think another reason was the simple joy in Paige returning to WWE considering that most of us have been expecting a "we wish her well in her future endeavors" statement for Paige for much of the past 12+ months. After all, how Paige was conducting herself in her personal life was embarrassing to WWE and her relationship with Alberto Del Rio, or El Patron if you prefer, was beyond toxic. Del Rio frequently made heated statements blasting WWE, some of them broadcast live out over the internet, sometimes broadcast during telecasts of other wrestling shows, with Paige in full view while it was going on and not doing or saying anything to calm him down. There have been rumors that Paige has been battling drug problems, as she did flunk a drug test, and her very public problems with Del Rio have been the centerpiece of her life. Also, let's not forget about the sex tapes of her with Xavier Woods, Brad Maddox, both at the same time, Maddox squirting his goo all over her while she was holding the NXT Women's Championship, etc. In a nutshell, Paige's life had become one never ending TMZ story in which it looked like she had flushed a very promising and fulfilling career in the biggest wrestling company in the world down the toilet because of stupid personal choices, the dangerous combination of sexually explicit material & the internet and a volatile relationship that was growing worse by the day. So when her music hit last night and she came out on stage, I think the reaction was also one of relief in that she hadn't destroyed her career, she had/is in the process of getting her life back on track and that maybe we weren't witnessing the next great wrestling tragedy.