I would look at day length as the primary reason. I posted the following on another chicken site but rather than retype I'm copying and pasting:
Once pullets commence laying, they go like gangbusters through fall, winter, spring and summer. Then, normally the second autumn and every one thereafter they will molt, which ranges from 1 to 4 months depending on weather they do a hard or soft molt. A hard molt will be obvious, a soft molt not so much.
During molt they lay very few eggs, if any at all. It takes a lot of protein and energy to grow a new winter down coat. So, aside from the super laying one sees the first year or two of laying, production drops year after year.
A broody hen won't lay any eggs. Because if she did, that would cause a staggered hatch and dead embryos when she abandons the eggs to take care of the chicks.
The broody hen won't affect the others' production. They don't choose to lay eggs. If they are in production, they'll lay eggs. If a hen is in their favorite nest, they'll either choose another nest, climb in with her and lay, wait till she comes out to eat or lay somewhere other than a nest. But if in production, the egg will come. It's an ovulation cycle that can't be willed.
Day length is a major factor in egg production. With shorter days and having older birds, production usually slacks off. Adding light will help with this.
Recently, I had 21 pullets and hens and was down to one or two eggs a day. 7 were POL so I didn't expect much from them. 4 were broody. 2 had been attacked by predators so were stressed. Most of the rest were molting. I actually had to buy eggs for the first time in almost 5 years. Bummer.
Molt is a normal process and providing more protein during molt can help them build feathers faster.
Another way to help your chickens through molt is to reduce stress as much as possible. Try to avoid handling your chickens, and bringing new birds into the flock, if possible.
I think when people begin a new flock with new birds and they lay so well for a year or so, it creates expectations the birds can't meet as they age.
It's tough for areas where we're limited by law to 3 to 5 birds. We spend a lot of money and time to keep the flock and still have to buy eggs. It creates a situation where we either keep pets that feed us fewer and fewer breakfasts over their life or choose to cull and start with a new flock every couple years.
A lot of breeds will produce 150 to 300 eggs or more a year for the first couple and then fewer and fewer every year thereafter.
IMO breeds that take a break and only put out 150 to 200 a year, and we don't add light and they don't get taken by disease or predators will continue to feed us for many years but don't be disappointed when they shut down for a quarter of the year.
