Games usually do their biggest numbers during release date hype.
Hype can make people do stupid things and make them spend money they didn't even want or expect to.
Even IF it takes a month or two to be cracked, that's two months of impatient pirates waiting day after day for a crack, not seeing it and possibly caving.
Even if that works for only 1000 pirates who couldn't hold out, £50x1000=£50,000.
Now, since this is GTA, this game could easily shift a million units on PC in a few months. Probably even more. Steam has many multiple million concurrent users online at any time.
If we assume that only 1% of those million units come from people who would pirate, but can't and give in to the hype or simply dont mind paying for a GRA game if they can't pirate it, that's 10,000 people. £100,000 in sales.
If theres a chance to not throw away tens or hundreds of thousands of <insert currency>, they wont.
Money is money.