Interesting. They do all usually shed within a week or so of each other. I didn't know it was environmental, always thought it was related to growth.
All animals shed their skin, humans included. For vertebrate animals (such as reptiles like snakes or mammals like humans) the primary reason is to replace the skin as it gets damaged, no to accommodate growth. Animals with exoskeletons do primarily moult due to growth, but their skin is a skeleton so it is designed to last, while animals which have internal skeletons have disposable skin.
If snake skin shedding was mainly about growth, adult snakes would only shed every few years, and often wouldn't shed at all after about 5 years of age, but even when they're not growing or feeding at all they generally shed their skin a few times per year. As with humans, it is primarily about skin maintenance.
Yes, snakes are very heavily influenced by their external environment, particularly temperature, whether it's natural or when we change their enclosure settings and bring them into or out of winter cooling etc (that's usually synchronised in a collection, so their hormonal cycles are too). It's a good idea for snake keepers to learn about this. The shedding synchronisation is also often due to feeding schedules, which tend to be synchronised within collections.
"But, Sdaji! If humans shed their skin, why don't we see it? Where is all this human skin?"
You can find plenty in your vacuum cleaner after you clean the house. It's not the majority (it's a common myth), but there's still a fair bit of human skin making up that dust in the carpet. A lot gets washed down the drain when you shower. If it gets caught in your hair it gets called dandruff. Humans completely shed their outer layer of skin and replace it about every 2-4 weeks, from the top of our heads to the soles of our feet, some parts even more quickly, but it's constantly happening in tiny pieces so we don't tend to notice it.