Most people I know in other industries get paid time and a half or double time for doing overtime because there needs to be some incentive to pick up the extra work.
NCP used to be a theoretically derived hourly rate of pay, which was then actually delinked (reduced) by being frozen for several years many years ago. These days, 1.25xNCP for a pp24 scale pilot is actually just a couple of percent higher than their normal rate of pay. This is why the company is finding itself needing to pay 1.5x and also offer buyback, in order to attract any volunteers. Whilst NCP was historically derived from the pp24 scales, it is the same rate for a pp34 pilot. So it is actually more lucrative percentage wise, for a pp34 pilot to do overtime than it is for a pp24.