They didn't live up to their own responsibility and caused others to lose out too. The disaster He found only leaves. Appearance of life but no fruit. Hendriksen in his Matthew commentary. Budding precedes leafing.
Small figs precedes the leaves, which precede the regular figs.
He sees nothing but leaves. It is the small figs which guarantee the normal figs. If there are no early small figs, there will be no big figs. So he curses it. It is showing by its nature that it will be as it has been - i.e. unfruitful.