No points upgrade to the Tower room allowed anymore?

I have booked a harbour-view room (cash) at the Main House and asked the hotel to upgrade it to the same room on the Tower floor by using SPG points (I guess 2500 points?) But the property replied like below:

Thank you very much for the email. Please understand that our Towers section offers separated product from Main House and product is differentiate not only in room rates but also the added benefits involved. Therefore, with much regret to inform you that we are unable to upgrade your Main House room to the Towers section.

Should you are interest in our Towers section, we are pleased to offer our Towers Non-smoking Harbour View King Bed Room under SPG Member Exclusive rate at HKD $2506 + 10% service charge daily per room per night on May 19 – 21 for your kind consideration.