We do, kind of.

Note the links between Florida and the Yucatan peninsula. There are also some "hops" along the west cost of the US and many in South America.

Undersea cables make a lot of sense when you need to cover a lot of ground without a lot of interconnects in-between. For example, in the NE United States, the nodes are too close together for an undersea cable to make sense. There are many points of connection very close together, with well established infrastructure that can house the cabling on land. On the West Coast, you have long distances in-between without much infrastructure. For example, between LA and San Fran, you've also got Big Sur. There's nothing requiring a fat pipe in that distance, so running a cable out to sea means not negotiating perpetual land-use rights all the way up the coast.

Land is cheaper when you are running though developed areas. But these areas of Alaska and Canada are desolate, you would first have to develop them and that is way more expensive then running undersea cable.

Also, I speculate that undersea cable is more resilient to seasonal freezing and thawing.

I don't know US geography that well but it isn't a universal rule. Africa (cheap labour + under developed), for example, has many coastal cities linked by sea not land.

The eastern seaboard of the U.S. is much more hospitable and stable terrain. Alaska includes some pretty gnarly mountain ranges and a fair number of glaciers.