By being more transparent. They announced the May 2nd media date a long time ago. A whole lot of people assumed that with that kind of lead time that Disney was going to open the ride within a day or two of that event. They assumed that because this has been Disney's MO for as long as I can remember. That was probably the original plan, since the date aligns with a slow time at WDW.
The result - people booked vacations around that date hoping and expecting to be able to ride this attraction this week or next.
When it became clear to Disney that this was not going to be the case, they could/should have made some sort of announcement so patrons could adjust vacation plans where possible. They did not do so because they did not want to lose the revenue during a relatively slow time of the year.
To avoid problems with FP+ you just need to announce the opening date 3-4 weeks in advance, but it could be months in advance - the longer the lead time, the better.
Are you telling me that they just found out today that this ride was not going to be ready until 5/28? Let's be real - they knew a long time ago. They delayed the announcement to avoid lost revenue.