[nell]

Their infrastructure might very well be setup in a way that can't scale.

They don't need unlimited scaling for the entire site, just enough to scale for one particular plane.

They make money from ads and subscriptions. Any such business pays for user acquisition and a % of users convert to subscriptions.

Even if all this is spiky traffic, their site probably has now had millions of first-time users. When traffic dies down, they will settle back at a higher than previous usual levels.