Admitting culpability more or less admits financial responsibility as well.

If Boeing would say "we're at fault", people would sue them (more than now) and have greater chance at winning those lawsuits, since Boeing already admitted to being at fault.

I can imagine Boeing, and the Boeing CEO, is trying very, very hard at walking a fine line of not admitting being at fault, but also saying that they are "taking responsibility" (since they have 300 souls, public opinion, and lawmakers against them). They have to convince people (those that matter, ie those stopping operation and sales) that the MAX and Boeing are safe.