Too much nitrogen in the soil and using manure are the main causes.

Thanks, what can I grow to exhaust my soil. I have used a lot of compost on my veggie beds in recent years.

Nature will do it for you. When you have a very wet summer, more nitrogen is made available from the soil, hence why a lot of plants this year are producing lush growth.
Garden compost is good for all soils as a conditioner/organic fertiliser. Just don't overdo it on your carrot beds. It's the make up of the soil....preferably nice and sandy...that is important for carrots so that they get a nice deep root run, and regular watering.
And it's why in the crop rotation system, carrots and other root crops always follow the brassicas, that need a lot of nitrogen and manure to get the best results, hence more of it will have been used up whilst growing them, meaning it'll be ideal for carrots the following year.

Thanks. That makes a lot of sense. I will do better next year.