There are a few reasons that this lack of creativity persists>
1: 'new ideas' are not endless. as soon as something 'new' pops up, anything semi-similar to it may be perceived as biting off of it in some form. therefore, new ideas can only be used once if they are to be both new and successful. there are exceptions of course where a product can be both a rip off of something and successful, if the original was a rather awful rendition of a great concept, and the biter just took everything good about the concept and delivered it better.
so reason 1 in a nutshell: creativity is not endless.
2: the stuff that game devs., writers, directors, etc. make has to be SELLABLE. in the end it comes down to whether people will be willing to buy it. that's why rarely do you see fresh new ideas turn out successful on a large scale. societies have 'societal norms' and things outside of that norm are usually shunned away with disapproval. stuff that is disapproved of by the majority of a market (the ppl you try to sell to) is destined to fail. and quite frankly, the market in the u.s. and in many other parts of the world is comprised of millions of people with conservative societal norms. for example in one of the zero punctuation reviews (GoW2) yahtzee pointed out that the game market consists "those emotionally fragile retards that make up 75% of the world's consumer base". though the exact figure is not really known, and the word retard is more figurative than literal, he does make a point nonetheless that games have to be made in way that "those emotionally fragile retards" buying it won't be disgusted by any off-beat-ness, subsequently giving the game a good rating.
reason 2 in a nutshell: it has to be socially acceptable if you want people to buy it
3: some ideas are used over and over repeatedly, because in the eyes of the market, they are good ideas. again, quoting yahtzee from the GoW2 review "it's worth remembering that sometimes popular things are popular for a reason - because they're good." which really means that popular thigsnare popular because it fits firmly within societal norms and excells that the things that society deems to be amusing.
reason 3 in a nutshell: the things that society likes are the things a smart company will try to sell because it is more likely to profit
damn, that was a long reply
and there are probably other reasons that new stuff doesn't come out but since new ideas aren't endless, i'll let someone else explain them