Earlier this month, WhatsApp started offering video calls of up to 4 people and now it plans to extend the limit twofold. However, given the feature is still in beta, it might take some time to reach all users. There’s also the limitation of people using an old version, something that is probably taking care during the test process.
Given how Facebook positions WhatsApp as a messaging service to your closest friends and family, the extended amount of people is probably just to allow more people to join social distanced evenings, dinners, and celebrating holidays. The platform is unlikely to try and take on Zoom, Google Meet or the likes for now.