So LANL is making weapons now. That used to be done at Pantex. Why is LANL doing this?

The US forgot how to make nuclear weapons. It's been decades since the US built one from scratch. For about 20 years, the US lost the capability to make H-bombs. There's some special material required, and the 1950s factory to make it had worn out. An attempt was made to make it by a cheaper new process, and that didn't work. A plant using the old process wasn't funded for decades.

The US has way too many old nuclear weapons, and has been overhauling them during this period. There's no shortage. The fissionable parts don't wear out, but the tritium has to be replaced every decade or so.