For me careless often lead to typos, ungrammatical might look incoherent. Failure to communicate is when people do not listen to each other not based on message quality.
Since I misread your message it was your fault for not communicating it clearly.
If you wrote something like this:
Most seniors I worked with had poor writing skills. They were failing to communicate because of lack interest in effective communication.
I would be unable to interpret you in different way. You either made you message ambiguous or you are shifting the goalpost.
