The rest of us use Facebook or Messenger to organize events because there's a lot of us and it's the most convenient mechanism for organizing group activities. If people choose to opt out, it's up to the organizer whether they want to go through the additional mental effort of communicating everything to the Luddites through whatever special communication method they require.

Mostly, we just require the Luddites to find out about events and updates themselves. (Usually they find out by overhearing the rest of us talking about upcoming stuff as its being planned.)

The end result is usually that the Luddites get themselves back on to Facebook after 6 months of missing out on shenanigans.