Because it would make taxation system simpler and fairer (by getting rid of council tax and business rates), and save a phenomenal amount of money.
I propose that local government be entirely abolished. I expect the cost savings would be huge.
Clearly, local government fulfils some important functions, such as running schools and emptying our bins. It would be perfectly possible to transfer those functions to central government, and no doubt it would be more efficient to do so, because of economies of scale.
Some local government functions could easily be axed. Seriously, how many people would be disadvantaged if your local Diversity and Community Engagement Team (no, I'm not making that up, my council really has one) ceased to exist?
At a stroke, we could abolish the council tax. This is not only expensive to administer, but is widely considered to be unfair (particularly to pensioners). Obviously some of the money would still be needed to fund bin collection, schools etc, but that could be raised by increasing income tax (leaving most people better off as a result, as the costs of doing things centrally would be much less than wasteful local government). Same goes for business rates.
Defenders of local government will point to the democratic accountability that local government gives us. But in reality, it's a complete sham. Much of what local governments do is dictated by central government anyway. And where local governments have discretion to do things their way, I see no evidence that democracy works in any meaningful sense. If you think local democracy works, then consider this: of the councils that have decided to go for fortnightly bin collections, what proportion of residents in those areas were in favour of that change?