People have been canning food for centuries and the processes uses have stayed pretty much the same over the years, except that they've gotten easier.
Canning nowadays is not only more intuitive, but fewer have had to rely on cookbooks; instead, they learn from friends and family which could suggest that canning is a technique that's passed down in many cases.
Overwhelmingly, it seems that canners prefer the water bath method for fruits and the pressure canning method for vegetables. With a process that's been around for as long as canning has, it's no wonder many have caught on to the ways that work best.
For more hard numbers on canning, check out the below infographic.