I play the game every day and usually have a pretty good score. it changes regularly on the old site.

I have been playing on the new site 99% of the time and I too wonder why I do not change rank or even how it is scored. 
Not really paying attention to the ranking as I just play for fun but if you get a top 10 rank on speed for 3 or 4 days out of 7/8 one would think your play was good enough for a rank adjustment. Hell I have not even been reading these forum posts. Maybe it is time to try and learn something. A concise explanation of scoring and ranking is needed that is easily understood. 

Like Fred and Chris, I was also wondering, why our ranking hasn't changed, on the new site?

Mine finally changed after a long time. Not the same way of computing it seems and you benefit of you've been playing a long time and all the games