WhatsApp broadcasts act a little differently than Telegram channels; they end up as normal messages in a 1-on-1 chat with each recipient (with a megaphone icon next to it), so it's not something you can join or even have as a separate section.
WhatsApp groups can be set to act like channels, however, by changing permissions to allow just group admins to send messages.
https://telegram.org/tour/channels
In this case it's more relevant to ask why Twitter or Facebook haven't been blocked (if they haven't).
I think WA has a similar feature ("broadcast") but not as widely used (since it is limited to 256 people).