To save time and money. To save a waste of fuel, and to enhance the lives of all citizens.
I know that some verge cutting is necessary, but a lot of it is excessive, in my opinion. Where wild flowers flourish so do bees, which are essential for agriculture, and horticulture. Apart from that, beautiful countryside lifts the spirits, attracts tourists, and generally improves a sense of wellbeing. Sometimes when the verges are slashed back, all that is revealed is brown grass and litter.
People often want to escape to the countryside, so why destroy it? It is costly and a waste of time. Perhaps once a year would be enough in a lot of cases.