Top employers (big tech; Amazon, Google, FB...big industrial; GE, Boeing, GM...big finance; Goldman, Morgan Stanley, JP Morgan...big retail; Walmart, CVS...etc) love engineers coming out of top 20 MBA programs. They compete with one another to hire this type of talent. Naturally, salaries for these positions rise.
The engineering background tells them you're technically competent. Top MBA programs are difficult to get into; coming from one separates you as intelligent and highly motivated (the latter much more important).
That's not to say motivated, competent, intelligent people must be engineers from good b-schools. Most people I know with those characteristics DO NOT have this background. But those quals are a good indicator and are easy to spot if you are a big company looking to hire talent.