the crims are not stupid, nor do they lack money
The implied assumption of the 5idiots, uh, 5eyes, is that the 'crims' will only ever use 'commercial' encryption tools, and as soon as the 5idiots prevail upon the tech companies to compromise their encryption, it will be all sunshine and daisies.
what is to stop well heeled crims from getting their own tools with encryption that doesn't have the shiny new backdoor in it? "oh, no, it's illegal for us to not have a backdoor in our encryption technology, we better stop our other naughty activities."
All this posturing and pouting like children when they are told "no" ignores the fact that the crims are not fools, they are well heeled, and many of them are very very smart and can write software.
Sure, it's not a "good idea" to write your own encryption algorithm, but there are plenty of examples of code out there that are quite robust that could be incorporated (without backdoor)