PTP is mainly designed to work well on LAN. While it can be used on WAN, there is currently no equivalent to the large quantity of open NTP servers on the internet. Thanks to the open NTP servers, NTP bring service comparable to GPS regarding time synchronization source, something that PTP is unable to do if you don't have access to particular master PTP node, usually connected to a GPS or a NTP server.
Maybe one day PTP will have a range of open master node on the internet, but AFAIK this actually not the case. It should be noted that when used over WAN, PTP is not better that NTP from the precision point of view.
Finally PTP don't solve all issues. To have a reliable actual time and time processing capabilities everywhere around the world, NTP, GPS and PTP should be extended to broadcast the updated historic leap second table and the updated timezone database, as well as the UT1 frequency offset. With all the additional information, any devices could use the right time for his purpose.