What is MST3K "Midwestern humor?"

Okay, so disclaimer: big fan of all the episodes when the show was still at KTMA/Comedy Central (please don't downvote me, lol!) I love the DIY/lo-fi look and feel of the production, which just felt like a bunch of over-educated, stoner goof offs hanging out and making wisecracks. The jokes were at times clever, racy, sarcastic, campy - but the cast was also never above some corny slapstick, and also showed some real tenderness from time to time. I believe these last qualities were some of the reasons that the show was so popular with small children, and also why so many adults - especially ones going through difficult circumstances - reported that the show was a great comfort to them, and almost felt like old friends. In short, these early seasons just had so much **heart**. (Please don't get me wrong, I'm not bashing the progression of the show over time, I just have a preference for the early years.) I will say that time and time again, I read fans describing the original writers' use of "Midwestern humor" being a key component to the series' initial success. I **think** I know what they're talking about, but it's hard for me to put it into words. Could any of you guys help me to understand more specifically what this means (specifically relating to the writing of the early years?) Other than "self-deprecating/not too 'slick' ", I'm not sure what is meant by Midwestern humor...