Is ‘it’s’ the most ubiquitous error in contemporary communications?

It’s understandable. Unlike most punctuation, ‘its’ has never made sense to me. Why doesn’t it have an apostrophe? Surely it should.

The dog’s comfy new rocking chair

Its fancy new rocking chair

The ‘it’ is just a stand-in for ‘the dog’; so if it’s ‘the dog’s’ rocking chair why isn’t it ‘it’s’ rocking chair? Surely it should be. Nevertheless, it isn’t. But it’s amazing how many people – even word-professionals – don’t seem to realise it.

I saw it in The Guardian recently. Almost fell off my rocking chair.