Your App is successful because you didn't spend time on useless things like a11y, i18n during the p-m-f stage. If you look at every successful product in history, they didn't focus on a11y or i18n right from the bat. Now, that it is successful, you can think about it and spend resources.
Now, this is why I like to see such things regulated with law. Because then a competitor, who spares the effort to care about, say, a11y, doesn't get ahead, but is instead punished. It's not that a11y is a bad consideration, it's that creators are badly incentivized.
If you become really big, you get x amount of time to implement a11y. Good enough balance.