This is not unusual especially for the Yosemite location. A couple of suggestions,
1 - Try a hotspot from T-Mobile that uses their new LTE Band 71. This is the new 600Mhz band that is supposed to reach further and shows as being available, on their map, in Yosemite pines RV resort.
2 - There is a really good YouTube video from a full time RVer about getting campground wifi using Ubiquiti network gear for about $100. The video is from David Bott and he gives a very detailed explanation of how to set up the wifi extender antenna.
Hope this helps.