It’s the brand NASDAQ, first and foremost. It isn’t the only index where there is only one option. DIA is the same (and similar exp ratio). Dow Jones is even simpler than the NASDAQ, you might say, why not just by those same 30 stocks and call it an ETF, but you cannot without infringing on their (S&P Dow Jones) product.
Just because you have the recipe for something you can’t make the exact same product, slap the same name on it and make it slightly cheaper. It wouldn’t work for Twinkie’s it doesn’t work for investments. You need to license the index from an index provider and then you can distribute. NASDAQ charges for that right. Plus as others said, in the grand scheme of things, 0.15 is still low cost.