Granted that they've at least tripled MAU since, but that's the power of network effects. There's a heavy dose of "in spite of" rather than "because of". On the other hand if Meta tried to, say, merge Whatsapp and Facebook Messenger, I think they'd lose half their users overnight.
Similarly, if Meta bought Zoom (and kept it running as it does today), most businesses probably wouldn't switch. Zoom already owns the market.