Dragapult is not mostly a physical attacker. It doesn't have a proper physical ghost stab outside of phantom force. As such, it's most common set in gen eight ou has been specs where it has all the tools it can possible want. Thunderbolt, flamethrower, hydro miss, whatever. That doesn't say it isn't used but physical Dragapult, whether band or dd, does pop up from time to time and those things do tend to use clear body for that exact reason. This is often effective as towards the end of the generation, Landorus uses special defense to somewhat check Heatran. In gen nine ou, it's more or less the case but clear body on it's become rarer now since Landorus is no longer as common due to competition with Great Tusk. Also, infiltrator is just a damn good ability because it bypasses screens and I believe also substitute while clear body has a limited impact
In short, infiltrator just has more uses than clear body and Dragapult doesn't have a wide physical movepool to use anyway
