Ideally mobile devices in theaters, malls, and stadiums aren't traveling at hundreds of miles an hour with a vantage such that they're in range of multiple towers simultaneously. It used to be (and maybe still is with 5G) that adjacent cells used different channel pairs. That way a handset at the edge of cell A could talk to both cell A and B to negotiate a handoff. Handoffs can happen pretty quickly.
If cells A and F are on the same channel pair and a handset can see both towers the tower the handset is not talking to just has a higher noise floor. It's like in an apartment if the next unit over is on the same WiFi channel.
You'll note that in older generation cell systems theaters, malls, and stadiums were terrible places for cell signals. Now many have micro/nano cells that cover much smaller areas to deal with congestion. Handsets reduce their output power when the received signal strength is better. So a handset will readily talk to a microcell at a stadium rather than try to talk to a tower further away (with a worse signal).
But for planes, hundreds of passengers hitting dozens of towers simultaneously on the same channel pairs would be rough on switching. Carriers need to know where in the network to route messages to handsets. If a handset is handing off to multiple towers quickly or worse hopping seemingly randomly to towers as a jet flies over it'll be difficult to keep it connected. Multiple that by thousands of people in the air at any given time. Areas near busy airports would have absurdly unreliable connections for people in the air and on the ground.