Apple and Google don't compete on phones, because they've each intentionally built incompatible ecosystems.

See earlier comment about consumer devices.

Office suites have Google sharing an MS Office-compatible suite they purchased. Apple has MS Office on its platform. But no real competition or innovation.

Who aside from Microsoft runs a gaming platform?

What looks like open competition gets a lot narrower in overlap once you look at the details.

Which is exactly what you'd expect, if you allowed companies to get too big and too dominant: they're not dumb, so they strategically rig the game in their favor to disadvantage new entrants, while carteling with similarly sized peers to ensure everyone mostly stays out of each other's pools.