According to the Lindens:

As anyone who has been here long knows, Second Life is a world that is constantly evolving and changing. Many of those changes are a result of growth. As our population has continued to grow, we are finding it is taking longer to process weekly stipends. Traditionally they have always been paid out on Tuesday. This is not changing, but you may find they do not show up in your account until later in the day on Tuesday or possibly even on Wednesday in some cases.

When I last checked, premium account numbers are dropping.

So why would it take longer to process something that's less of a challenge?

Maybe because it's just a declining service among growing billable services like the LindeX, tier processing, and island fees, so it gets de-prioritized?

Nah. That's just nutty. Just one of many tasks and services and obligations that are having scalability issues. Marketing and Phil talk about hundreds of millions, but the tech goes kablooey when sixty thousand wander the grid.

But I do like SecondLie's take on it.