Curbs

Today my workout consisted out to practice to take me out for curbs and down the verdict. Not the easiest directly but I will probably get better at it so eventu on ie. I've probably passed on at least a thousand times today feels like but tomorrow my goal is to not tip over as many times.
Over the past year, I've always wondered why there should be so high and so many curbs here and there. But I have never received an answer to my question. Is there anyone who might know why there are so many curbs here and there outside? Once you have come up with a sensible answer so please tell me the answer for me, I'm very curious about that answer! :)
Have a nice day!
Xoxo Snowman on wheels