Because Microsoft wasn't interested in their customers but more what was in their pockets... They knew full well they were releasing a faulty product but hoped that some miracle would happen and all retail 360s would be ok...
Sorry to be the one to tell you this but I think your blu ray drive has packed in. This happened to my 60GB PS3. If its in warranty you've nothing to worry about but if not you'll have to pay 250 quid for and out of warranty exchange, and they'll send you a refurbished one. Pricey I know but what else can you do.