Because the rich bastards in the Conservative party and their mates with all their dodgy offshore holdings don't give a toss if the UK is destroyed economically. It either won't affect them or they have enough money that it will barely leave a scratch on them.
That said, I believe that it isn't that cynical for the key players. It's more about ego for the likes of Farage and Johnson while Dominic Cummings is just an anarchist who wants to prove something to himself so I suppose it's about ego for him too.