The 2.4GHz band is an ISM band, Industrial Scientific Medical. This is unlicensed spectrum in which licence-exempt equipment may be used, your WiFi is suitably tested and CE marked as is their baby monitor I expect.
Microwave ovens leak a lot of energy when they're running, but generally the gaps between pulses are sufficient to keep WiFi and Bluetooth operating.
The problem you are experiencing is expected in a dense RF environment.
Zen Fibre 2