Full length wetsuits, whilst being warm, are relatively unpopular in kayaking. The tight rubber around the arms and shoulders can be restrictive for the repeated motion experienced in paddling. They are sometimes worn during surf kayaking though where the possibility of being repeatedly thrashed by the waves can make a full suit more appropriate.
Farmer john style wetsuits , so called due to their appearance similar to a farmer wearing dungarees, are more popular as they combine the benefits of a wetsuit on the bottom 2/3 of the body with unrestricted arm movement. Some of the warmth of a full wetsuit is sacrificed in order to free up the arms.
The combination of a farmer john style wetsuit and a spraytop is a common starting point for people taking up kayaking in milder months. Beginners tend to be in the water more often that experienced paddles so the wetsuit is a practical garment in these circumstances. If you go to a club or outdoor centre to learn kayaking you are likely to be issued with this combination for your early training.
Many kayakers progress from this type of outfit onto drysuits / drycags etc and develop their own preferences for the type of garments they prefer.