It's not that simple. Yes, they have to act in the best interest of the shareholders, but they historically have had great leeway in determining how to do that. It doesn't necessarily mean (as in this case) releasing your most-experienced but highest-paid employees in order to drive down costs. Note especially that keeping costs down never comes up in discussions of executive compensation or how much lawyers get paid.
It's actually been only the last few decades that there's been a push to define corporate responsibility as exclusively toward shareholders as opposed to other stakeholders including the employees and surrounding community.
I agree with this. I personally work for a large, publicly-traded company, and I found it very enlightening a few years ago when senior management described having three groups whose interests the company needed to keep in mind: customers, employees and shareholders. That's a very useful way to think about companies in general.
Some companies put customers first. Zappos is a frequently-cited example here, and I'm sure there are others.
Some companies put employees first. Google gets this reputation, as does SAS. Tech companies do this a lot, especially when employees are also shareholders.
Some companies put shareholders first. Frankly, I think this is probably most companies, and it's understandable.
A well-run company will find the right balance of the three interest groups. You certainly have to take care of shareholders, but if you screw employees that will be bad for shareholders in the long run. The same goes for screwing customers. One argument I've heard is that it's rare to have long-term (as in decades) shareholders of companies any more, which means that shareholders tend to think in the very short term (since they don't plan to still be shareholders in six months' time). That's bad for the business in the long run, but if the current owners don't care about the long run, well, it's understandable.
Management is hard. It's possible that WotC is leaning too far toward shareholders and not far enough toward employees; I honestly don't know.