It is simply not logistically possible to vet the machines prior to tournament day. The tournament directors who make the final call on playability of each machine live 3 hours away. The machines are dispersed over an area of a few hundred square miles, and only show up in one place on setup day. The owners of machines typically provide their assessment ahead of time, but as many know, tournament players (including the tournament directors) are much pickier than some machine owners and operators, and machines don't always show up in the condition the owner thought, often because the machine was in storage for the past year.
Last year, only two of seven machines in Classics bank, and 2 or 13 machines in Modern bank, had the glo balls. Far from your statement that more used them than not. What is the difference between having steel balls and two machines where one has strong and the other weak flippers, or two machines with same strength flipper, one has steel ball the other glo ball? Either way, when you step up to a machine, you need to adjust to how that machine plays.
Ultimately, you don't need to play any of the machines with glo balls during qualifying. If we use them, it will be a minority of machines. In the finals, one of those machines can end up being selected if you don't have machine choice, but then that just proves someone else wants to play the machine with the glo balls. Just like with super-bands, rubbers on outlane posts and setting, ball savers, and so many other adjustments that can be made, it's up to each one's individual preference what they like and don't like for setup. And like all those items, glo-balls is just one more tool in our arsenal that we will use if needed to create a better tournament experience for the majority of players.
One idea I had was for a machine we choose to use glo balls, have the glo balls in half-the-day, silverball in other half, but still combine all scores. Then we'll really see if they have a positive or negative effect on scores, and let each individual choose if they want to play that game with a glo-ball or silver ball. Not doing that this year ... but the thought has crossed my mind! I'd put my money that more people prefer the glo-balls on those machines where we chose to make that switch.
Oh, to keep things fair on Twilight Zone and powerball mania, we will replace all silverballs with glo-balls; powerball mania for everyone all the time.