It's not about what features are and aren't included.

You offer different plans to make one sound like a bargain, you offer an expensive one to make the others look relatively cheap and you offer a cheap one too. No-one chooses the cheapest wine.

It's a human psychology thing, nothing to do with features. If you aren't using this trick, you probably shouldn't present it like that as it's confusing.

You can use support levels instead or something to make an expensive premium plan if you want to take advantage of this marketing 'trick' that everyone else uses.