Sorry, you're way behind everything. The large majority of pensioners are well above the pension credit threshold (though that may depend on what "just above" means).
The big problem is that we paid N.I. to fund the pensions of pensioners then, not our own pensions in the future (which now is now, and funded by current taxes).
Without replicating the Four Yorkshiremen sketch, most pensioners now were brought up in houses without central heating, in colder winters than now and waking up with ice on the inside of the single-glazed windows. More seriously, pension credit is demonstrably the best way to deal with pensioner poverty (with commensurate savings in health costs), and raising the pension credit threshold would be a much better use of money than giving it to the majority of pensioners who don't need it - it might even pay for itself in saved NHS costs, so I'm not sure why that could not have been a sweetener for this awkward policy.
(And no truck for the people on here who would not give pension credit to anyone who hasn't "paid in".)