Why did I have to create a new profile after the move to Nexus?

You do not need to create a new profile. If you try to login with your original pcdmisforums email it should work, just will ask you to update password. Many people have transferred over so far. If you could not post on the transferred account, but could login.

Try this on your other login https://nexus.hexagon.com/community/public/pc-dmis/b/news-and-announcements/posts/how-to-get-started-in-pc-dmis-community

Nexus is what happens when sales critters are in charge.  You're shown everything except what you came looking for. 

I did exactly as the instructions said to do and I still can't post anything on my old login.

I had the same issues with the account transfers...I'm guessing someone fixed my issue for me since one day I was able to reply and post in threads once again. I never got a response as to what the issue was though.

I followed the instructions to the letter and it didn't work for me either.

You're really missing the point here. This is better for us. And we must have wanted it. 
I find the janky navigation, inept search tools, and aggravating format to all be quite endearing qualities of this new and improved experience. It's like an unexpected adventure during this road trip we call work...  

The search functions and structure here is actually horrible. Might make sense to me if I started drinking again but I don't want to go down that road...lol. 

You're brave being able to say exactly what I've been thinking and keeping to myself. You are the true unwavering baron of Nexus.

i liked the old forum better

Try going and changing your password again. I had the same problem and couldn't post until I changed my password.