They set them up to prioritize 5G; and while that might be fine for the majority of people, it can sometimes suck for those of us who live on the fringe. One example - say you've got a tower within a half mile that's still 4G, and a tower 2 miles away that's been upgraded to carry 5G; your phone might want to camp on the marginal 5G signal instead of the stronger 4G. Was the same kind of thing happening when 4G/LTE was being deployed; people were turning off LTE to stick on 3G... until it finally caught up.
As bob said above, 5G vs 4G distance depends on which band it's carried on. The really, really, super fast 5G is on millimeter waves, which carries a ton of speed and bandwidth but garbage distance and building penetration (sometimes only covering a block or two). Most 5G outside of major cities is deployed on the same bands that 4G was and has the same potential coverage distance... it's just not nearly as fast (faster than it's equivalent 4G, just not significantly faster).