Suppose someone owns £1m house - just picking a number. They work hard for the next 5 years, earning a decent whack of say £100k a year and pay around £170,000 in income tax and national insurance. Quite a lot of money by nearly everyone's standards.
Then they need to move to a slightly larger house down the road so one of their 5 kids can have their own bedroom. The new house is £1.1m. They have to pay (In addition to all the other moving costs) ANOTHER £50,000 in tax out of their savings that have already been taxed.
God help them if they wanted to move every 2 or 3 years because of their job, paying £50,000 every time.
Honestly, I think it's ridiculous and people being worse off than them, does not make it sensible.