cross platform mechanics like this are not difficult as you think to implement, just because it isnt done often, does not mean its impossible or difficult, its just most developers dont care or dont see a reason to spend the resources to do so, this question becomes more complex if you talk about direct play, but sharing simple content in the same game across platforms is not all that hard to implement.....the only really questionable thing is performance, as the blueprints could get quite complex and might could be hard to run on consoles depending on this, but honestly, its the same concept with PC as well, as not everyone has powerful gaming desktops. but the PC audience is more understanding of performance dips.
most games dont have crossplay as there can be an advantage in a lot of titles using a mouse and keyboard, though some games where that isnt an issue do it, Rocket League for instance is cross play with PS4, XBOX and PC....all those platforms play together.
