This is the response from South Eastern
Thank you for contacting us today about our new station Thanet Parkway. I'm sorry to hear you are unhappy not all services stop at this station.
Thanet Parkway was envisioned to be part of the high speed route, offering direct journeys into St Pancras. Whilst there is a route that goes from Ramsgate to St Pancras via Dover Priory, it isn’t the most direct and so the focus of the first timetable for the station was via Canterbury West. This meant that when we wrote the timetable for the Canterbury West routes, we kept the stopping time in hand so trains could call at Thanet Parkway now it’s opened without interfering with timings elsewhere along the line. This wasn’t the case with the Dover Priory route, though, and so it’s not possible to add the extra stop as the extra time would cause problems at Ramsgate, particularly with the time needed for trains to turn around there.
But as this is a new station, we’re still learning how passengers will look to use it. We’ve set the current service based on our expectations, but if we start to see demand for different journeys through Thanet Parkway, we may be able to make adjustments in future timetables.
Thank you again for taking the time to contact us. I hope the information I have provided is useful. However, if you have any further questions please do not hesitate to get back in touch.