Because those A/V transmitters used the same 2.4GHz ISM band as WiFi at the time, there was actually no regulatory protection against this interference - from a regulatory perspective it's just a normal and expected part of using an ISM band where there is no protection. The increasing popularity of WiFi started to really surface the problems in this area, similar issues are seen in 900MHz far less often because it's mostly used with low-power, low-duty-cycle devices.... the same as was intended for 2.4GHz before widespread consumer WiFi.