The average farm makes £40,000 profit per year so the value of land is probably the only vehicle they have to sustain the business (by borrowing money against it). Without this, no farmer can afford to farm. If you need £100k of equipment and supplies then you're going to struggle to borrow on profit alone. Those profits have also struggled massively due to cost rises over the last 5 years.
I actually disagree with these assessments of land values because most farmland is only worth its value as a farm. If a farm only makes £40,000 per year and the land costs say £1m then that isn't a viable business that anybody would buy. Farmers are the only potential purchasers because a farmer sees a farm as more than just a business which is why they indeed don't just quit to work 9-5.
Either way I think the logic is pretty simple. Would everybody like to pay more for their food? No. So do we need farmers to succeed and lower their costs? Yes. Is the government making it easier? No.
I'd understand if this raised £50bn but it won't, it'll raise around £500m maximum, city will pay more for 5 players. The return to the treasury is meaningless so it's nothing more than an ideological tax. It'll raise even less in the end because most affected farmers will take advice and give up their ownership and put their land into discretionary trusts in which case IHT doesn't even apply.