Why? The ability to fly off a carrier was all that Harrier had over Tornado in SDSR
Easy street
Come on now fella - the Harrier had a couple more advantages over the GR4 than just carrier ops.
Its VSTOL ability allowed it to fly from short rough-field strips near to the front-line, providing rapid close air support (CAS) - hence the ability to operate away from conventional paved runways and airfields which may be attacked, preventing conventional non V/STOL aircraft from operating. It also had no LOX requirement and was able to take ANY aviation fuel... and before the 'helpful stacker' pipes up i am talking RAPID response.