Apparently, the NCAA considered this, and ended up deciding that it wasn't feasible. One element of that is that it really isn't under the control of the NCAA. Keep in mind that postponing or cancelling wasn't really the NCAA's decision. They were still planning to go forward without fans when a number of schools and conferences, including Duke, Kentucky, and Kansas, informed them that they would not participate in any tournaments. It was only after their hands were forced that the NCAA decided not to play in empty stadiums.
And any decision to reschedule would similarly be subject to the schools' participation. Most NCAA member universities are closing down their campuses entirely, likely for the rest of the academic year. Until they reopen, there's no way for their athletic teams to come together for practice or much of anything else. Reopening campuses isn't something that the NCAA has any control over, and they likely would have faced a situation where some of the schools that would be invited to tournaments likely would not have done so, leaving them with an incomplete field.
That's on top of the logistical problems of trying to find venues and all of the other problems of rescheduling.