(as a former U 89 owner, endorsing what 0vu said) Try listening over headphones and tapping on the body of the mike to get an idea of this. All that a manufacturer can do is put the capsule on the end of a somewhat flexible "stalk" inside the capsule head. Its material has to last for decades without deteriorating or stiffening. And the stalk has to be short unless you make the capsule head extra large. So the total benefit that can be had is rather minimal--a few dB of isolation at best.
When Neumann introduced the U 89 their idea was to create a more versatile successor to the U 87, including its being smaller and lighter. I don't know whether you've ever seen the actual capsule of a U 89 but it's oddly about twice as deep as any of Neumann's other capsules. If the microphone is dropped or struck, the capsule can smash against the screen, distorting its surround and ruining the tension setting and the distance to the backplate. One of my U 89s had visible waves (regularly spaced wrinkles) in one of its membranes when I bought it on eBay, which is a symptom of this type of accident. Unlike most other manufacturers, Neumann doesn't repair capsules, so the only remedy is to replace the capsule.
Thus there's a narrow limit to how soft an internal suspension can be. And if the body of the microphone is vibrating for whatever reason, the capsule picks up those vibrations acoustically anyway. (Imagine being trapped in a bell tower--one of my favorite older mystery novels has that as the method of murdering someone.) All in all, "internal shock mounting" can never substitute for a shock mount that isolates the entire microphone and some length of the cable attached to it.