They only reap it if they move to a cheaper area. Your proposal would just make it even more expensive to move home . eg. A couple living in a flat have a child and want to buy a larger home in the same area would find it even more difficult than it already is.
Second or investment homes are already taxed at about 30 of the profit. Whilst that might seem fair on the face of it I'm not sure it does the market a lot of good since it deters people from selling investment properties and decreases availability, pushing up prices and reducing the number of taxable transactions.