Microsoft would make competition harder by bundling "good enough" versions of competing software into Windows, with business deals restricting pre-installs of competing operating systems (if you pre-install Windows on 100% of machines, you'll get a massively better deal than when installing on it on 95%), and (arguably) by making interoperability harder by not having stable documented interfaces and having the interfaces change with new releases every few years.
That was bad. But Apple... Apple hasn't been just making competing harder, but outright impossible. It's one thing to compete against a free pre-installed product. It's another thing to try to compete when the platform owner straight out forbids you from shipping a product that competes with them, or applies draconian business terms to the competition that their own business units get to ignore. They weren't just making interoperability harder by not documenting interfaces, but (in the case of iMessage) by actively breaking any attempt to interoperate.