They do all the time, and have done for years.
Do you think we should make all smokers who get ill pay the £hundreds of thousands it costs for a protracted cancer treatment plan?
Should all obese people have to foot the bill?
Where do you draw the line - I assume only responsible well behaved people should ever get free treatment?
Those things may yet prove necessary, if the NHS isn't to cripple us all. Or end up privatised. Or totally dysfunctional.
Esp people who ignore their doctors advice; act against their own best interests; and have the financial means to pay for their own treatment (ie, aren't poor).
Those people have no moral right to go cap in hand to the NHS for free treatment.