PMing is a private thing. Most people want to be asked in the public forum if someone can PM them anyway and making sure someone is a legitimate user who cares about the forums is important and to many, this means seeing that you've not only been here a while but are participating.
There are many who will make an account just to PM people for sources, only to report those sources and get them removed, thus harming the people here in the process and removing their agency and choice to die. People on here have to be careful and I'm sorry if this is frustrating for you and I, too wish it didn't have to be this way, but it does for the integrity of the forum. It's a small measure that can help users to see who cares and is genuinely interested in this cause.