It’s something people don’t often recognize but it’s true in two days.
1. Reputation - A LOT of people were anticipating their debut. The first news about Aespa trended in Korea and China. Even if the public wasn’t up to date with all the debut details they know of SM’s legacy of debuting successful girl groups. And to many of them Aespa (then known as White Fox, Moonlight Angels or SMNGG) was going to be SNSD’s spiritual successor.
2. Fandom - Aespa debuted at a perfect time when other SM GG fandoms were more accepting of them. At fx’s debut they were under prime SNSD’s shadow. When RV debuted they faced fierce hatred from fx’s fandom. But by the time Aespa debuted these fandoms mellowed out. Sones who didn’t give fx and RV that much of a chance checked out Aespa. fx fans no longer have a group to look forward to, so it was either RV who they initially hated or new girls Aespa. And SNSD/RV fans with company stan inclinations saw Aespa as an opportunity to get back to former SM glory days.
While many factors went into Aespa’s success, these two were two major foundations from where they could grow higher more quickly.