Parliament has shown precisely zero interest in debating IR35 reform
Well yeah. Contractors are an easy target, and while they may moan they can be easily dismissed as rich workers trying to tax-dodge. That's an easy sell to the old voters that matter. The alternative is to look to other areas to tax -- wealth for example. Now there is loads of money in wealth (houses, pensions, dividends, etc) that if taxed properly would mean a government could offer decent public services. But the instant you try to take any of this money you are waking up the daemons that will rouse the old voters and kick you out.
Over time this is getting more tricky as we are an ageing society, with the dependency ratio falling year on year as there are fewer workers compared to the growing number of old, sponging (sorry, claiming their right to draw a pension) off the state. Why do you think they recently said NI was to be increased, rather than look at taxing property at death?
You dare touch the wealth of the old and you will soon be out of office. That money is for the kids, not for somebody else. Politicians are not stupid.
 Drawing a pension is acceptable, being given benefits (spit) is not. Guess who encourages that message.