Rob and Sean Were Co-Chairs of Their Student Union's Fundraising

Rob and Sean were co-chairs of their student union's fundraising committee.Their task was to raise a substantial amount of money to repair and remodel the student union offices.
Over a month had already passed since they sent out a letter to their alumni, but so far they had received only four responses and pledges for a total of less than $200.They were expecting a huge return because they were sure they had written a good letter.
Rob and Sean made sure that their letter was clear, short, and to the point.Knowing that most alumni would have fond memories of their university, they didn't go into a lot of detail about how important it was to renovate the offices so up-to-date technology could be installed.And they didn't want the alumni to think the current students had been neglecting office upkeep, so they didn't go into a lot of detail about all the upgrades needed.Instead, they focused on the amount of money they needed and how much they wanted from each graduate.
What went wrong? How could Rob and Sean improve future fundraising letters?