Or maybe they could normally keep lower performing employees around, but cash is getting tighter so they decided to let some of them (less than 4%) go.
"Cash being tight" and "firing some employees for performance reasons" are not mutually exclusive.
Low performers (and especially the bottom 2%) can often provide negative value to the company. It's quite possible there is no net additional work to distribute, or if there was, that they had additional capacity in the rest of the workforce for the same tasks.
They may not need to be replaced. If they do, we can safely presume they determined those resources (cost / time) involved in doing so were less than what it takes to replace them.
It may not negatively impact their production rate. They may be able to improve their production rate by spending that money in a more targeted way now.
"Cash being tight" and "firing some employees for performance reasons" are not mutually exclusive.