Public Footpath sign

I saw this sign during our country walk today - not long after we'd seen a young lady riding a horse along this path! Anyway it occurs to me that in the UK people are excessively keen on telling others what they can't or not allowed to do - it's all very negative (I wouldn't want to try riding a bike along this path which was along the side of a cultivated field Even if I did, what harm would it do?)