http://jakonrath.blogspot.com/2014/04/a-wake-up-call-for-tracy-hickman.html It's OK I'll just wait here for you if you want to go read it.
Oh Great! You're back! The author of that blog post makes some strong valid points, but part of the problem is that Tracy mostly got their following by writing Dragonlance novels. The following is for the Dragonlance brand, and not for the actual author. In addition to the advice given in the blog post I would suggest that Tracy Hickman diversify their writing and writing platform.
Here's what I suggest to avoid this problem:
1.) Market yourself as the brand along with the series name. Sometimes if you have a tie-in like Dragonlance, it's easy for readers to get lost in that. They may not realize that they may enjoy some of your other works. Which leads right into #2
2.) Write other stuff! If you have a series that is popular then by all means continue with it as long as you can. At some point all good things come to an end, so be prepared! You need something to fall back on in case something happens. Each novel is a building block in your arsenal. You can continue to experiment until you have another work that gains traction. Then you can build another series that can provide another revenue stream.
3.) Get the word out! Tracy Hickman claims to have a six million reader following, BUT Dragonlance has that following. Tracy should have struck while the iron was hot and built up an email list that they could use to promote their other works when the time came. Does Tracy have six million email addresses on their list? I suppose it's possible, but considering they are complaining about not making as much money I would not think it likely. This also includes getting on all the relevant social media outlets if they are not already present.