The reasoning behind this is that some shady landlords might try to claim that genuine tenants are squatters in order to get rid of them. There are plenty of desperate people who'd accept a verbal contract and payment in cash, after all. Not that hard of a choice when the alternative is being homeless. Oh, but you paid your rent a day late? Sorry, you're now a "squatter", so we're cooking you alive until you leave.
Making it too easy to get rid of squatters would expose the most vulnerable people in society to even more abuse, and making it trickier for absentee landlords to get rid of real squatters is considered a fair price to prevent this.