We are mainly riding road bikes on flat paved roads. Therefore, the tires of road bicycles are smoother, which can reduce rolling resistance and increase your cycling speed.
At the same time, to reduce weight, road bikes usually use narrow tires, and its tire clearance is much smaller than the gravel bikes. Generally, road bikes are fitted with tires in the range of 23-28mm.
Gravel bikes, which can support up to 50mm tires, and usually use wide tires with tread blocks. They need to deal with more complex roads to provide better passability.
But this also makes gravel bikes on paved roads speed down, so some riders will install a set of road bike tires directly for their gravel bikes.
In other words, gravel bikes can be compatible with gravel tires while also meeting the installation of road tires, but the road bikes may not be able to install gravel tires.