Maybe a very distorted type of theft but from my perspective the main immoral thing about theft is that it deprives someone of what they used to have, or takes the place of a sale. From the limited research I've seen the evidence is, at best, mixed that corporations are losing sales due to piracy.
If it was a clear choice between buying something or pirating it, equating piracy with theft would be more reasonable (though the owner still has their good so not entirely identical) but that doesn't seem to be the typical scenario. The ads only make that equivalence because it's better for the companies if they convince people it's theft.
From a moral perspective I think whether it is theft really depends on your motivation/what you would do in the absence of piracy.
If it was a clear choice between buying something or pirating it, equating piracy with theft would be more reasonable (though the owner still has their good so not entirely identical) but that doesn't seem to be the typical scenario. The ads only make that equivalence because it's better for the companies if they convince people it's theft.
From a moral perspective I think whether it is theft really depends on your motivation/what you would do in the absence of piracy.