That appears to be what is happening.
There have been recent tensions between the two organizations, including a recent lawsuit. It doesn't appear that they are best buds.
The Sands group (majority Mavs owners), in recent PR interviews, has been showing off their Asian resort/casino property. They have been lobbying to legalize gambling in Texas because they want a resort/casino as part of their new entertainment complex.
Gaglardi, the Stars owner, is Canadian, but his mother is a native Texan, and he still has family in Texas. In an an interview I saw a couple of years ago, he suggested that brick and mortar casinos would be a stretch for Texas.
My speculation...Sands seems to have a much higher priority on gambling than Gaglardi does, and Sands is going to have to create a significant amount of local political turmoil to make that happen. Given that Gaglardi has Texas ties, he may not want to be part of that mess. I think both groups have different "entertainment" philosophies, and are going their separate ways.