You're absolutely right. Since Delta Episode deals with space and meteors and general Nigel deGrasse Tyson stuff, it makes sense that Deoxys too would a part of this. Another horrifying implication is that Deoxys purposely wanted to crash land and be a general d-bag and kill people and stuff, so you catch it to control it. This helps in the Pokemon WiFi battles that people have ( basically the meta game), as Deoxys has been quite popular. So as why Jirachi wasn't allowed is because Jirachi has connections to the moon ( I forgot what, exactly), but the moon doesn't come much into play here. Maybe, just maybe Nintendo wants to hold an event for the evasive Jirachi. Something tells me Deoxys too would have ended up an event Pokémon if not for the story line of the Delta Episode and to help trainers in the meta game, which is gaining enough popularity that hope full GameFreak and Nintendo start paying more attention to it. These are just my thoughts on the matter, and the official raisins may differ lol
