The guys on top were not wearing any safety harnesses. Imagine one slip while tying the banner. Also, by a simple lever-arm mechanism, if the workers on top leaned to one side of the scaffolding, a turning moment would be resulted and the scaffolding would just topple and there was no way the 4 guys at the bottom could prevent it, even if they were at the base and trying to hold the legs down.
If the company used those aerial platform, not only would it be safer, they could also save the 4 manpower at the bottom cos you can control the wheels from the top. Oh well, better equipment means money.