I'd be totally pissed if my car could not be serviced after 7 years...why should we be happy this is the case with our photo gears?
It's a manufacturing fact of life -- as much as we may not like it. In a way, part of Planned Obsolescence. And it DOES hit cars as well. I have 2007 Land Rover LR3. About three years ago, the key for the trailer hitch attachment broke off in the lock. It necessitated them drilling it out and hobbling together a make-shift release because they no longer manufactured the part and no long had stock! My reaction was somewhat the same as yours. I was told that, generally speaking, when something goes out of production, for warranty purposes, the companies are only generally required to provide service and parts for 5-7 years. When parts run out, it creates an end of service. In the case of the 400/2.8, it is/was a low volume lens. On the other hand, lenses like the 50/1.4 and the 85/1.8, which have been in production for 20-years, remain serviceable. But just because a lenses has reached end-of-life, doesn't mean Canon won't clean, adjust, etc. They just did that with my 27-year old 300/2.8. There was a disclaimer that no parts were available for repair if needed, but they cleaned and adjusted the lens.
Finally, I owned the 70-200/2.8L. I now have the 70-200/2.8 L II (and have for a number of years). Get the Mark II. Unless you plan to stick with lo-res camera bodies, the quality and resolving power of the Mark II version is astoundingly better. If you don't believe me from actual use, check out DxO.