I don't know if it's old blokes who get blasé, particularly, more a state of mind that some people develop ... a bit hard to explain exactly, but you see it a fair bit - they pay lip service to checks, cut corners.
Certainly no reflection on what may or may not have happened in this case - I know I've been distracted at times only to get a frightening wakeup call when I realise I've come close to doing something stupid. As was said at the start, it can happen, and none of us are immune.