On second thought I don't think it is to avoid spam, because today I have seen around 10 spam messages, which have already been removed, created by users without models and without reputation. These users had created the message and also a response in the message without problems (I don't know how old those users will be).
@skapricorn, the external links from the last post I created today, don't work and it's impossible to follow them because they don't look complete. This was not the case in the other messages that I created days ago.