IP infringement and theft are different things, infringement is often done in regards to IP that is in the open, if I hack and steal your trade secrets which are by definition secrets and not protected by a patent what is that then?
And in any case you are arguing about semantics, "theft" is also technically not a singular legal definition but an amalgamation of different civil and criminal legal statues.
In most jurisdictions intangible property also does fall under the broader definition of theft:
https://en.wikipedia.org/wiki/Theft
