Here's a list of the Long Trails in the US.
There are some east west ones. Here's a selection...
The American Discovery Trail goes coast to coast. No one does it.
The Pacific Northwest Trail. People do this one
The Great Enchantment Trail. Andrew Skurka has done it as part of the Great Western Loop but I hadn't heard of it until now.
In the East the Allegheny Trail is basically East West. Lots of people do this.
There are a few other loop trails which necessarily have East West sections.
While the big 3 were inspired to follow mountain ranges that is not the only criteria for a long trail. In general these other trails, East-West, or not are not as popular/well known. I'd guess it is mostly lack of funding for them. Even the big 3 are barely funded. They may become more popular as time goes on since long distance hiking has become more popular. In the nineties there were probably only about 200 long distance hikers a year on the PCT...it is hard to say for sure... with about 40 a year claiming to finish. Now, 2020 excepted, there are around 8000 long distance permits issued, with 4000 through hike permits and over 1000 claiming to finish according to the PCTA.