The developers make TPT in their free time.
This means that if they are busy, they cant develop TPT.
Updates are still made, just look on github.
You can also compile TPT yourself, to take a look at the features of the current source code.
Look at the Github page for it.It might seem like just bugs and new elements,but there's a lot of bugs,and bug fixing can take a lot of work (finding the source of the bug and fixing it both can take a lot of time)