A ban would reduce the UK water companies income. They seem to prefer to hold off imposing a ban at the risk of having to impose a much stricter one later, or even having to ration supplies.
It was a good call in 2018 for just when an increasing number looked inevitable, the rain came.
Apart from the risk of having impose stricter bans, or even ration supplies, later, this seems fair in that really poor people would not use much more water while the very rich with big gardens and lawns (and water meters?) would pay more, and be able to do so.
Of course this depends on people having meters.