You're generally not wearing just a drysuit if the water is cold. Under the outer shell, you often wear multiple undergarments to keep warm. Think a base layer, underwear, socks, 1-piece.
I once did a cold water dive in a drysuit without fleece undergarments.
We were loading our gear onto a charter boat for a week's dive trip and the boat captain dropped his keys through the dock and into the water. I volunteered as tribute, threw my drysuit over my t-shirt and jeans and went down in search of the keys.
I quickly found the keys which was a blessing because it was the coldest I have ever been; I would never do a drysuit dive without the layers again.
We were loading our gear onto a charter boat for a week's dive trip and the boat captain dropped his keys through the dock and into the water. I volunteered as tribute, threw my drysuit over my t-shirt and jeans and went down in search of the keys.
I quickly found the keys which was a blessing because it was the coldest I have ever been; I would never do a drysuit dive without the layers again.