DTG just wrote on their TS homepage forum asking for things to take into consideration for the future of the development of TS. And also stating that
“This won't be the last time we do this. Despite the age and breadth of add-ons available for Train Simulator, it is a living platform and as such worth looking both backward and forward in terms of improvement.“
So i think that at one point DTG thought that TS could just be put nicely to rest. Indeed @Maik Goltz at one point said that only one person was working on TS, while the rest was transferred to TSW. But now they seem to have changed their mind, and are putting work resources back into the platform.