The UK couldn't afford to operate 500 low-cost fighters. The procurement cost (say £10bn-ish) of the aircraft is irrelevant - 500 fighters is (say) 50 squadrons, which means ~20 airfields with base maintenance facilities, supply, fuel never mind the drivers and their initial/currency training.
Fast jet pilots are supposed to have something like a minimum of 160hrs/yr (with the RAF working to a higher figure) to remain current aren't they? So 500 sortiable aircraft means 500 pilots, which means 80,000 fast jet operating hours per year just for currency (never mind ops). Even if we just take the manufacturers figures the direct operating costs (at ~£2500/flg-hr) would be over £200m/yr. Then factor in the additional 20 airfields, the drivers, the airworthiness organisation to support them etc etc.
This is way more than Mr & Mrs Taxpayer are prepared to fork out for the Royal Airshow Force.
PDR