Why do step parents suck so much? (long story)?

Ok so in my case I am living with my mothers husband and he annoys the living crap out of me. I don't even want to come home from school anymore because he got laid off of his job so he just does nothing and it bothers me because I do eight hours of hardwork in school, then do the house work too. When He does nothing but sleep in, watch tv, play on the computer etc. It pisses me off everytime I come home he is sitting there playing on the computer while I am cleaning. he could at leat help out some not a lot but some. Me and my older brother both can't stand him he's 25 and has his own place and I am 17 stuck living here. What pissed me off today was when I took out the trash and came back after a bad day of school he had the nerve to say I don't do any of my chores and I clearly do, so I got angry and talking back a little and called my mom because that made me mad. My mom said that she would talk to him but I don't think she is. I just wish it was just me and my mom because he causes so much conflict. I also hate it when I am talking to my mom and then he trys his best to interrupt my conversation with her it's so annoy. I don't like him mainly because he is very childish, I will give you an example over winter break when he was working I came out of my room to get some breakfast I go to get the orange juice that my mother paid for and top is screwed on tight so I am thinking it wasn't like this yesterday and my mom would do that so I put hot water on it to make it easy to open and it worked. Then when he saw me with it he started singing " one more year one more year" because that's when I graduate. So when I told my mom to talk to him he said that he got the song from a sifi show. Which I know was a lie I think he is out of his mind he just do stupid stuff for attention. My question is if you have a step parent at home why do they suck so much? here's my story if you like to share yours then comment Thanks and sorry for the long story