I don't know any more about this case than anyone else who watches the news, and make no assumptions about what happened, but I do (unfortunately) have experience, going back over many years, with planning authorities and can see why some people may be tempted to ignore the rules.
Basically, there are 3 ways of getting planning permission.
1. Have very good local political contacts
2. Hire very expensive lawyers and hope for the best
3. Bribe either planning officers or planning committee members.
People (and always the same people) often get planning permission when they shouldn't, simply because of who they know, or because they happen to be married to a councillor or similar. These people simply put in an application, which is either approved by the planning officer under delegated powers, or recommended by them to the planning committee, who simply rubber stamp it.
People who can spend a fortune on the very best specialist lawyers (who shouldn't need them for straightforward applications) improve their chances, but basically ordinary people and small firms can't afford them.
People who have lived and worked in an area for many years can usually find out which planning officials and which councillors to approach for option 3. It isn't even always necessary to ask around, some of them make it clear.
Even when there is no corruption involved, which must happen sometimes, the process takes forever and costs an enormous amount of money.
So, developers can find it much easier, quicker and cheaper simply to have a fire, knowing that the insurance companies will have to pay out unless they prove that the owner was involved in the fire, which can be difficult