To add to @spaeder answer here's a more detailed explanation, in your case you have the most extreme case:
* [https://www.ifixit.com/News/12903/flexgate|The Design Flaw Behind MacBook Pro’s “Stage Light” Effect]
* [https://www.ifixit.com/News/13979/apples-2018-macbook-pros-attempt-to-solve-flexgate-without-admitting-it-exists|2018 MacBook Pros Try to Solve Flexgate Without Admitting It Exists]
And a vid which also goes over it as well [https://www.youtube.com/watch?v=iLALpD004Gk&t=76s|The Design Flaw Behind MacBook Pro’s “Stage light” Effect!]