I've done this too but it got me right on the sternum. God it hurt. I should have been wearing body armour. Dangerous business this gardening lark, people should be warned.
Can be, like anything, it's whether you take precautions that matters, like looking where you are walking, learning how to operate a piece of equipment, wearing gloves etc etc.
Generally you will probably be gardening alone or with a partner, with no other human input to cause you accident, when cycling you have all manner of "in coming" to deal with.
And I think they are warned, every piece of gardening equipment or chemical or whatever will contain on the label a warning for the operator to read.