If they don't want to do prep and collaboration, they shouldn't DM/GM at all. My first time running Shadowrun was at a mini-con, waaaaaaay back in the days of the Universal Brotherhood just being exposed. I'd written a detailed run where the runners were all prisoners of KE, given a chance to commute their sentences by taking out the hive and getting data back to Ares (yea, I'm as surprised that I was spot on as you are).
Very Dirty Dozen (or for you millennial-types, Suicide Squad), but I allowed them access to some of their gear, just not their contacts. To this day, I'm still not sure if I was just frazzled from my first Convention GM or that the player came up 2 minutes before start, but I missed that he had a grenade launcher built into his cyberarm. I had the entire hive planned out, very maze-like with lots of techno-organic horror (think Aliens) to get through, fighting through flesh-forms and true-forms to get to the queen in the center of the maze. They go in, and this dude makes a terrific perception test with his thermographic cybereyes, then launches a grenade a the wall, blowing a hole through it and avoiding the maze to get to the queen. Then they (mostly him) kill the queen with sustained fire and grenades (did I mention a maze that was going to eat up resources?) in just a few rounds. I congratulated him, thanked the players and learned the lesson that players will always turn left when you plan for them to turn right.
Unfortunately, regarding GMs, they bring in personal bias with them all too often. The perfect GM is someone that works with the players (think "yes, and?") instead of just monitoring whether they are "breaking" the rules. I've run into a number of Shadowrun GMs at various cons that seem to live by the notion that they are experts at the game and, by having the GM title, whatever they say goes. Many times, this results in the least fun games I've ever had, and they turn into Gatekeepers, preventing new people from wanting to invest in the game.