It's Career Inertia.
For half a century CIA hired people who had invested massive resources in becoming completely fluent in Russian, well versed in Russian culture, and who had cultivated contacts in Russia. These are the sorts of skills that take a lifetime to develop. All of the most senior staff at the intelligence agencies fall into this category.
This is why the intelligence agencies stick their fingers in their ears and sing "LALALALALALA... I can't hear you" every time Chinese intelligence humiliates them. They're a one-trick pony: anti-Russian operations. That's all they know how to do. They're just trying to get to retirement, no matter what it costs the country.