I wonder why these first-home grants (many countries have them, Australia, Canada and New Zealand for example) don't say - use this but only for a house within

I wonder why these first-home grants (many countries have them, Australia, Canada and New Zealand for example) don't say - use this but only for a house within 5% of government valuation. That way, the price can't be inflated. Sure - for now, many may not be able to bid on a property but once prices start to fall this should make sense.