Why aren't they getting new content then I should have said? How does cross play have anything to do with that? Seems like both sides are being petty.
The Better Together update is meant to
- consolidate Minecraft's ongoing development
and
- unify its communities across all platforms.
To that end, most versions of the game are being aligned to a common codebase, where updates can be pushed simultaneously and with parity. The PS4 version is not, because it cannot enjoy the most major benefits of the Better Together update without the cross-play support.
One of the most important parts of the Better Together update is dedicated server support. Mojang will themselves supply four large dedicated servers housing infinite worlds which can support thousands of players at any given time. These dedicated servers will be backed by online presence. Websites, discussion forums, the like. These dedicated servers are cross-play, keeping them unfragmented and unifying the community in a big way. Dedicated server support already existed on PC and mobile platforms (and they're the reasons why those are MC's most popular platforms - online dedicated servers are Minecraft's defining mode of play). Now, they're not only going to be available on every platform - they'll be unfragmented. Anyone can join any server from any platform. That's huge for Minecraft and its overarching community. And so, Mojang would have to be willing to fragment that community, providing PS4-only dedicated servers with their own separate web presence, in order to enable some weak semblance parity there. Going against half the intent of this update/upgrade.
There's also dlc purchases, which will become platform agnostic and carry over to every other platform, but when purchased on PS4, they won't. There's local play and online play with other platforms in their worlds, which PS4 version won't have. And the Super Duper Grafix pack. Because the PS4 version isn't getting the engine upgrade, because it'd necessitate its own team to develop bespoke updates for a version of the game that can't interface with the rest of them, a version of the game that would need its own updates separate from the one update pushed to the rest of the contemporary platforms - a problem that Mojang is trying to eliminate almost entirely by consolidating MC development into one overarching version for many platforms.
So, in other words, it would be self-defeating for Mojang to spend the time, effort, and money to upgrade Minecraft for PS4, when Minecraft players on PS4 ultimately still would not be able to utilize the main benefits of the Better Together update.