Iyan in Leave

Can someone tell me why this plant leave spicies does not biodegrade as fast as other plant species. 

Growing up in Ibadan there was always complaints and public service announcements  against the use of this leave to package food by local food sellers as the leaves block gutters and storm drains. 

This leave is used to package a variety of foods including moi moi, eko, iyan, amala, eba the list go on. So now plastic is the normal.