Because they are done people who don't have everything that is required to apply yourself. But using an agent also means that they own your visa, so every time you want to do an extension or if you ha e issues with immigration, they will ask for a huge fee.
Do it yourself or ask someone in the group to help instead.
Contact the embassy. Both me (in Hong Kong) and my friend (in Hanoi) moved from processing to finished 2 hours after emailing and asking how our applications were going.