@Samdelila do you do know that means testing any benefit costs millions of pounds, don't you? You know, because actual people have to be employed to do the testing? And even if you could get a computer programme to do it, you'd still need actual people to handle the appeals, which would be many.
Quite often, benefits that rely on very few rules (state pension, for instance. Are you over a certain age and alive?) can be dealt with by computers so are relatively cheap to administer.
other rules like are a couple living together as a couple,or his he just a boyfriend that stays overnight on occasions, or, is the person's really incapable of doing what they say? Or are they over/under estimating their ability to function?
cheap benefits are those that are universal and have very few rules. Expensive ones are those that have many rules, some of which are very subjective.
I worked in and around the government benefit regime for 40 years. I know without a doubt, the fewer the rules, the cheaper it is to administer.
the more complex the rules (don't get me started on widows running starts and the rules around share fishermen, let alone 7th day Adventists) the more staff you need to administer the benefit.