system
Given the following post, respond as if you're commenting on Reddit:
human
[Evangelion] Why do emergency plug ejections nearly always fail?

What it says on the tin, basically. Minus Rei's ejection during Eva-00's testing, I can't think of a single emergency plug ejection that actually worked. You'd think with all the financing NERV gets, they'd at least be able to install a few backup systems.
gpt
For starters, the Eva units weren't completely finished. Eva-01 (Shinji's) was the prototype model; the appearance of the Angels started a bit before NERV forecasted. The Evas are also somewhere juuuuust beyond the horizon of human understanding and can't really be scienced into a perfect solution.

But most of the issue with the Evangelions were not technical in nature. There's a reason they tend to say that the Evas are "rejecting" commands to eject/activate/whatever, rather than "systems are failing." They and their neurally linked pilots very much have minds of their own and, though they can sometimes be forced into compliance by methods such as the dummy plug, NERV's control over them ultimately dependent on their cooperation.