Why do the most common winter tents not have floors? Last winter I camped a night on a lake and I woke up and had 2-3 inches of water inside. That night was not that cold and I did have heat. Our winters do not usually compare to northern Minnesota but last year we gave you a run for your money. The main things I worry about are the floor area becoming a muddy mess.

Thanks Darrell

Using any tent on lake ice is 'at your own risk'. The most likely reason for waking up with water in your tent while on ice is that there was a heavy snow fall shortly before that. The weight of the snow forces the ice down which then forces water up through the cracks in the ice.
The floorless tents are made so that you can dig a 'cellar' for the cold air to drop into. We don't often get enough snow to do this in my region so there is not much advantage in the floorless design, unless you use one for the sake of a wood stove. Using a stove can cause thawing and re-freezing that can freeze your floor to the ground. Then it's like packing up cardboard.

Agree. If you camp on a lake, you take the chance of dealing with slush. I typically don't set up on the lake. I prefer being back in the woods and out of the wind.

Winter tents don't typically have floors. In remote areas, where allowed, winter tenters will pack down the snow and line the floor area with spruce boughs. The boughs make a floor that allows anything spilled to pass through and any snow brought into the tent will melt through with the stove heat. In addition, you don't want your stove setting on a floor for fire purposes. If you are in the BWCA you can't use spruce boughs for floors, so you need a tarp, or tyvek, or matting of some sort to make a floor.

A typical winter tent will have a "border" at the tent bottom, made from some sort of water proof material. This is intended to be placed outside the tent and snow packed on top of it.