The files in question define tests for our hardware. In hardware testing, false-passes are the ultimate evil. A false fail can be dealt with (you just get someone to fix it), but a false-pass can make its way into production, un-noticed. Therefore, we'd far rather break modules that are currently seming to work, then to leave them with potentially hidden problems. Adding "use strict" is seen as a bit of low-hanging fruit.
--Dave Opinions my own; statements of fact may be in error.