US providers are expected to provide national coverage, in a country that has a much wider spread of population, while also being approximately the size of Europe. It's not exactly an easy area to cover.
Cellphone towers minimize the impact of density. Lower density and you can use fewer towers. The limit is one cellphone tower within 45 miles of you or 1 tower per ~6,000 square miles as they can have up to 45 mile radious ^ 2 * pi - overlapping area. Continual US is only 3 million square miles or ~500 cellphone towers. You do need significantly more towers for various reasons, but towers only run 250,000$ aka ~150 million to cover US own. However it's really spectrum and city's that are expensive not empty land.
In the UK, Three provides nationwide coverage + free roaming in 71 other nations (including USA)[0] for as little as £13/month for 4 GB of data.
On EE I’m currently getting unlimited texts/calls and 30GB of data (with roaming in EU and US) for £17.99/month (~$25/month). Makes US prices look crazy.
Three's coverage is garbage outside the big cities (and sometimes garbage in them!), and Feel At Home is never 4G.
Everything except Verizon is garbage in rural America.
They have a clause in the fine print, that says that you have to be in your home country at least once a month, in order to use this service. I thought it was great for me staying abroad for 6 months, but I could only use it for a little more than the first.