My best guess is that daylight hours are what cause garlic to scape. Similar to onions bulbing. It would also make sense because strong plants and weak plants scape at the same time. Some years garlic will come up a month sooner than normal other years it will be late, but it will always scape at the same time for that variety. I just noticed today that my plants are starting to grow scapes.
Most garlic is very similar but there can be a lot of contrast too. Cultural practices still affect it over time. It similar to having different strains of the same tomato, like Brandywine. There are new breeds of garlic. Seed companies do not work with garlic due to the difficulty of breeding it, but home growers, like myself do. I have several new garlics growing now. Two of them are in the garden from last year. I have 20 or so in the garage under lights right now as well. Of the ones under lights I might get 5 strong plants. I had sowed 500 seeds and that is what I got. So seeds and seedlings can have a lot of problems making it new garlic a rarity.
Here is a good source to learn more about true garlic seed.
http://www.ivansnewgarlics.com
He also sells garlic he has bred.
-Zach