A carrier in germany has to build 26 times less towers than a carrier in the US, because germany is more than 26 times smaller than the US.
I would think the increased expenditure of 26 times more towers would increase the cost of plans.
Europe also never had the culture of carrier subsidized phones, and so were never accustomed to paying more in monthly fees in exchange for low to no cost upgrades of hardware.
Tethering varies by carrier in the US - Verizon is legally obligated to allow tethering due to the result of a lawsuit, so they do not charge any extra for this, i believe t-mobile also does not charge for tethering, but it is not related to a lawsuit AFAIK
A final point is that pricing for data is fundamentally different in europe as i understand it. Most plans i am familiar with in europe tier data prices by speed - in the US almost all plans get the fastest speeds available, but it is tiered but amount of data used. You cannot pay for faster speeds on a typical US plan, only for greater amounts of data. The european side of that may have changed, as its been a year or so since i was last in europe looking into this