Without any spoilers for the new viewers:

The story implied in the first episode that they tried to make more advanced neural net type androids, and they all failed spectacularly compared to Vivy. They had the technology before, but they all failed until humanity found the epiphany of giving androids a singular goal. One that thankfully doesn't have to be all that specific, but it is the single command at the core of each of them that keeps them stable.

It's also likely that compared to her service-bot peers at the time, an exorbitant amount of money was put into Vivy when she was created that keeps her at parity with other androids produced decades and decades later until they reach a level of mass production on Vivy-type androids.

Why Vivy was created the way she was does get revealed over time. You also see the other androids over decades catch up to her, starting with the Sisters that are based off of her in the 3rd episode.