There should be property taxes for domain names, or at least purchased but unused. If I put in a serious bid to buy a site and the owner declines, they should have to pay idk, 5-10% of that bid for the next year or until a higher bid is made.
it should be expensive to buy and squat on a domain name that other people want. These domains are a common good allocated by society.
You might have issues of companies unseriously bidding on competitors sites to raise their domain property taxes. Maybe we need a related price to bid?