The kettle has a spout to ensure that the heat comes out of the mouth, so why is there a gap in the lid?

In addition to the answers of the previous friends, I think that the kettle and his lid from the point of view of the manufacturing process, if they do not leave a gap between them, or leave too small a gap, then: 1, to increase their manufacturing costs; 2, the lid may not be able to cover the kettle into the mouth of the kettle. 3, or even if the lid will be the kettle cover the kettle's mouth with other methods, and when you want to take down the lid, may not be able to take (can not be taken out). It may not be possible to take it off (not be able to take it out). (If you do not believe, you may want to do an experiment) 4, the kettle and its lid if they do not leave a gap between, or the gap left too small, when the kettle is in the state of being heated, and the owner for some reason to open the lid of the pot, in general, it is not possible to take down the lid of the pot.