Parscale's thing is the online operation that he's been telling people is super sophisticated and powerful. The kpop stan narrative might get Trump off the hook for being unpopular but it's no good for Parscale's brand.
The ticket reservations were more about building up a database for the campaign (and future fundraising lists) than about actual expected attendance, which is why he talks about getting cell phone numbers to verify. Can't come out and say that now because they spent the week before the event hyping their numbers. Plus all the microtargeting in the world won't mean shit if Trump's sitting at 35% approval in the fall.