"no good reason" is entirely subjective, though. If your purpose is to make the language simpler to newcomers, implicit conversions everywhere are a great way to get things done. And the popularity of PHP (especially for new-to-programming people) heavily supports that they made the correct decision to work well for that market.
The same kind of logic is used to make `false == ""` true. Or any 'falsy' language. If you want strictly typed behavior, yes, it's stupid to do that. If you don't, then it makes some things simpler, at the expense of more edge cases that are unlikely to happen - note that this bug was reported in 2011, and people are acting like it's a new thing. Because it comes up so rarely that, while it technically exists, many people never encounter it.
The same kind of logic is used to make `false == ""` true. Or any 'falsy' language. If you want strictly typed behavior, yes, it's stupid to do that. If you don't, then it makes some things simpler, at the expense of more edge cases that are unlikely to happen - note that this bug was reported in 2011, and people are acting like it's a new thing. Because it comes up so rarely that, while it technically exists, many people never encounter it.