why does social security take so long to make up their minds on a disabitly claim

i'm a 54 year old disabled male i have COPD emphacema and conjestive heart falure and i'm trying to get on full disabity i've been trying for 3 years now ad keep getting denided. i can't work anymore i'm on 4 lpm of oxygen 24 hours a day so i can breath. my question is i've been denided 4 times and my case went to a hearing judge . he denided it too so my lawyer appealed it again . now they say it's going to take 24 to 30 months to make a desition then was told after he desides it could take 12 to 24 months to get my disabitly pay that's almost 5 years and i've been waiting 3 years now . what i don't think is fair is i worked most of my life and i've paid into social security so when i need it like right now it will be there i hope you can help ne with this ,thanks David Ringeisen