Yea also, a few years ago I traveled around the entire US with a 4g hotspot and had service in nearly every place I visited, even in many remote national parks. With 5g being significantly faster than starlink, it does seem that this is an incredibly niche product.
National parks in the US are pretty well developed, and often crowded. You and I may just travel differently; my preferred camp sites are usually far away from cell coverage.
Cell service requires radio connectivity to a cell tower, which depends on distance and local terrain. It's quite common to have connectivity on a ridge or mountaintop, but lose it in a valley. Starlink works as long as you can see the sky.
Also 5g speeds in a suburban or urban area are significantly different from the wilderness. I have some property an hour drive from Portland. While some people can get a signal and their phone says "5G", the distance to the cell towers is great enough that actual connectivity is extremely spotty. It takes minutes to download a single photo. Starlink is much more consistent. You actually get better performance if you're farther from civilization.