Why?

2G (GSM) uses time division multiple access (TDMA).

The phone transmits in rapid 217 Hz pulses (on/off bursts).

3G (UMTS) uses code division (CDMA).

It transmits in a more spread-out way.

Less pulsing = fewer sharp current spikes = weaker ELF fields.

4G probably lies in between 2G and 3G, leaning closer to 3G’s behaviour.

5G is unpredictable.