The blog[0] explains their choices well. The brief highlights:
- Escape is simply unusable.
- Alt alone leaves the viewport and goes to menu, making further keypresses unregistered
- control is inconsistently placed on keyboards (e.g. laptops) which they don't say directly in the blog, makes extra sense if you recall it suggests not using devices the abuser might be admin/monitoring (public devices, friend devices, etc). It also is highly selected by other assistive technology products just like sticky keys.
They also recognized the issue... And tested it against JAWS and using it with on-screen keyboards
Seems they were very thorough.
0: https://beeps.website/blog/2024-10-09-why-govuk-exit-this-pa...
Note: this is the same link as in the grandparent post