Yes being flat does help for sure. In much of Europe I think they solve this problem with trains or sometimes buses to get to the parks or outlying areas. For example, much of Italy is hill towns and no one wants to walk up huge hills to get to each town but you can typically get there with transit.
The United States admittedly is quite large and spread out but if we started to connect more things with transit then I think it would stop feeling so much this way. Like why couldn’t there be a connection from San Francisco to Tahoe that doesn’t involve driving? It’s a very very popular weekend trip and a train would be great for moving skis and other equipment.
If you live near Seattle, you’re lucky to have some of the better planning in the United States and some of the more open-minded people with regards to transit, camping, etc. In a place like Florida, for example, it is fairly common to meet people who’ve never been camping unless maybe you count a music festival. The priority is often air conditioning, a nice hotel room towering over the beach, etc. which is not what the Dutch seek out for the most part