BlueTooth uses 2.4 GHz signals and they are attenuated by walls and other stuff inside your house. Outside the signals are not attenuated by as much stuff and will reach much larger distances.
Here is a web site that can be used to see the difference in distance in different environments.
My Samsung S21 Ultra (and most BlueTooth devices) should be outputting in the Class 2 power of 2.5mW (4dBm) and reach 10 meters in open air.
Normal BlueTooth should not have any issue reaching from one’s pocket to the HAs located behind your ears unless their BlueTooth antenna has very poor gain and it probably is very small and this may be the real issue.
My streamer will pick up my phones BlueTooth signal outside up to about 30 feet while it is in my front pocket.
I have a BlueTooth unit for my Arduino that is mounted outside and it has an 1/8" x 1/2" antenna and it will transmit and receive from ~ 50 feet including going through a three layer window.
I think the problem with the HAs BlueTooth has to be related to the antenna size and low noise amp in the HAs.