I think the point is that, if express ticket is allowed, people will 'farm' for event points differently. Also, do remember that energy is a consummable that can be bought, repeatedly.
Currently, the system allows express tickets to be used on any map that has been cleared once. So, in normal maps, express tickets are used to farm for equipment when playrs can only clear the map once, after using lots of consummables.
If express tickets are allowed in event maps, for example, the twin pillars event previously, players with weak teams can spend some gems to get to a slightly higher floor (eg, normally can only clear 35, but willing to spend enough gems to clear up to 50.), then spam express tickets for event orbs. And that's not really fair for other players whole don't have the capability to spam gems until floor 50 so they can "farm" event orbs.
For now though, due to the system set-up, allowing express tickets on events isn't really a good idea, but do keep suggesting, maybe there may be better ideas that makes event maps more easily clearable with express tickets without mucking up the system and causing everyone to feel that its unfair.
now that does make sense. But as I said before, only enable after all 3 trials is done.
Usually the trials on each harder level consist: not losing any unit or clear in x number of turns (even the player with weak team who can spend gems for many retries can't clear this trial).
well, I hope at least my suggestion open up developers / other people for better suggestion on express tickets. maybe my suggestion is not ideal, I hope somebody can perfected it.