As others have stated, it’s not about malice, but rather about miscommunication, misunderstanding or simply forgetfulness. It has happened many many times that

As others have stated, it’s not about malice, but rather about miscommunication, misunderstanding or simply forgetfulness. It has happened many many times that I thought I was clear on a thing and that everyone was on the same page to later realise that some of us completely misunderstood what was discussed or agreed. Sending a summary email afterwards helps make sure that everyone came away with the same conclusions. I’ve also found it extremely common that people simply forget things, or parts of things. I’ve had bosses who forgot that they asked for a change or feature or task to be completed. I’ve had bosses who forgot that they agreed to change a requirement or that something isn’t needed or important. I’ve forgotten that I said I’d get something done. I’ve had coworkers forget that they were supposed to do certain tasks. By sending a quick “here’s what we agreed to” email avoids all of these issues, or, at least, let’s you point at it later if someone questions it later. Basically, it’s a good idea to keep a log of decisions that were made.