It's the difference between an LFG and LFM post. I wouldn't take it as an annoyance.
A leader will post a LFM post and let people message them. It's the most efficient way to fill up a fireteam currently. It takes a TON of the burden off the leader to find a team. So instead of finding 1 person at a time, a lot of messages will be sent to the leader who is validating on their console. Thus why they ask for level, class, etc. and they will invite right then and there instead of looking back to FTW.in. However we are thinking of new ways to help make this a better process.