They show what's good for *them* to show you. Not what’s good for *you* to know (a thread).
You could get lots of impressions simply by tweeting a lot. That says nothing about the quality of your tweets.
Engagement Rate is a ratio of engagements to impressions.
If you have more Retweets & Likes (engagements), you’ll have more impressions, thus leveling out your engagement rate.
If your tweets are, on average, more engaging, you’re getting a higher ROI on your Twitter investment.
Their Analytics are deliberately confusing, so you'll get sucked into spending more time on the platform, rather than actually learn how to improve your tweets.