Briandg I understand why it is overwhelmingly no, although I am one of the few who voted yes. One of the major reasons Glock has been so successful is based on the idea that an external manual safety is not needed with their design, giving It the simplicity of a revolver with the advantages of a semi-automatic. I don't disagree.
I don't own a Glock, but I've shot a bunch of them. If I where a sworn uniformed officer carrying a service weapon on my belt or in the military carrying a handgun, I would be happy to carry a Glock. I'm not, and unless I am carrying a revolver in the woods I carry concealed. That adds another level of complexity that requires either a long DA trigger pull or a thumb safety for me.
There is an aftermarket, "Gadget" safety that enables a person to exert pressure with the thumb to prevent the striker from completing the cocking movement and the trigger being pulled. I think if Glock added this, or a thumb safety as options there are a lot of folks who would consider their handguns.
Glock knows their market. I doubt they will risk offending their base by adding safeties to a proven product.