The main purpose of the cowling is to improve the efficiency of the fan by preventing the air from being slung off radially.

https://en.wikipedia.org/wiki/Ducted_fan

Agreed, but failure containment is another of its purposes, at least on contemporary turbofan engines.

Did you ignore what I said and not watch the blade release tests?

Indeed. https://youtu.be/736O4Hz4Nk4 is a bit long, but they detonate some charges on a blade, watch it take out all the others and keep it all inside.