Here's why:

* Continental Crust: This is the thicker, older, and less dense type of crust. It can be up to 70 kilometers (43 miles) thick in some places, particularly in the oldest and most stable parts of continents called cratons.

* Oceanic Crust: This is the thinner, younger, and denser type of crust. It is typically around 5-10 kilometers (3-6 miles) thick.

So, while tectonic plates are made up of both continental and oceanic crust, the continental crust holds the record for thickness.