My understanding is that it was a software incapability issue with the original software. When the present owners took over the forums, they decided not to upgrade the site and port it to more robust software, so it continues to limp along.
Yes, there are others that allow direct messaging. I'm involved with another engineering forum, now owned by the original owner of Eng-Tips; however, if I mention the name of the forum this post will get deleted by management. It has direct messaging and a very friendly interface.
I'll see if I can disguise it....It is simply with an "i" instead of "y". Then add engineering.com...all one word. I think you'll like it.