Trains that trackmaster/plarail have not produced

Hi guys. I just wanted to say why trackmaster/plarail hasn't produced all the trains from the TV series of Thomas the tank engine. We all know that time when we were all looking foward to that one character to be realesed but it doesn't get released. I think this is a problem as there is many characters that we would like to be released so why aren't they making them
Here are the trains that have not been produced:
Smudger, 1 episode
Sidney, 2 episodes, 1 special
Millie, 8 episodes, 1 special
Derek, 1 episode
Norman, 5 episodes, 1 special
Fergus, 4 episodes
Rex, 1 special
Bert, 1 special
Class 40, 2 episodes
City of Truro, 3 episodes
Flying Scotsman, 1 episode
I am pretty sure I have coverd all the characters
But the sad thing is, most of the characters that have been made have appeared in 10 episodes or less and some of the characters on this list have been in a lot of episodes and specials and some of the characters on this list can be made from the other characters molds
Please reply about this issue.