The Travel Authorization form is no longer required and has been removed from the website. That is different than the form you can fill out on the plane.
The plane form, Immigration and Customs form (C5) can be filled out online in advance and was never required but encouraged.
The JTB states "Travellers will be processed through Immigration and Customs. For faster processing on arrival, travellers are encouraged to submit their Immigration/Customs card online at
https://enterjamaica.com and may do so at any time prior to arrival."