Let's take a quick example of a BA LHR-JFK ticket in Economy (because the average miles collector does redeem in Economy, and London to New York is a very typical redemption choice):
4-11 June, the BA Y fare is £358. This comprises £162 of 'fare' and £196 of 'taxes'. Of the taxes number, £108 is BA's fuel surcharge.
Anyone redeeming miles here would be sacrificing 50,000 miles for £162 of value - a ludicrously bad deal - and still be facing a bill of £196. There is something very wrong here.