In the Epic lawsuit it was shown that Apple really actually more cared about this than "security":
> “The #1 most difficult [reason] to leave the Apple universe app is iMessage ... iMessage amounts to serious lock-in,” was how one unnamed former Apple employee put it in an email in 2016, prompting Schiller to respond that, “moving iMessage to Android will hurt us more than help us, this email illustrates why.”
> “iMessage on Android would simply serve to remove [an] obstacle to iPhone families giving their kids Android phones,” was Federighi’s concern
> “The #1 most difficult [reason] to leave the Apple universe app is iMessage ... iMessage amounts to serious lock-in,” was how one unnamed former Apple employee put it in an email in 2016, prompting Schiller to respond that, “moving iMessage to Android will hurt us more than help us, this email illustrates why.”
> “iMessage on Android would simply serve to remove [an] obstacle to iPhone families giving their kids Android phones,” was Federighi’s concern