They can - you can switch to a variable direct debit. But for most people/households this is too confusing, or it leads to too many failed payments, so the norm is to try to even it out across the year.

got it, thanks. I thought it would be something like this, but it does feel like trading one complexity for another.got it, thanks. I thought it would be something like this, but it does feel like trading one complexity for another.