Before freshwaters made pearls so much more affordable, I suspect most women owned fewer pearls. Probably many women only owned one akoya strand. Such a necklace would be worn more often and so would need to be restrung more often.
With regular use, after a year the silk might fray or stretch. Silk readily picks up oils and dirt so then the knots turn grayish. Gaps might form between the pearls as the knots stretch out. All these are indicators that it's time to restring.
A number of us have taught ourselves to string and knot pearls so we can take care of the task ourselves, saving money in the process and avoiding downtime while the pearls are out for repair. Knowing how to knot also allows you to buy loose pearls and make your own strands. It only requires a few basic tools and thread is cheap.
Well I guess I am one of those women who only own one set of Akoyas so they will see lots of use! Restringing myself is looking like a great option! I really wonder why the pearling industry is unable to come up with a more permanent solution, because frankly it sounds like a pain. A stronger, non stretch thread that was also gentle on the nacre!