What is the difference in cost where you are? I can only get the 15% Finisher/Developer or the 20% combined Starter/Grower here. There is a $2 a 50 pound bag difference. Straight 16% Grower is not available. It’s possible that because of mass production the Grower is actually cheaper than the Finisher where you are. Anyway cost might enter into your decision.
In the commercial operations where they buy it in bulk, Finisher is less expensive than Grower because the protein content is less. Commercial egg laying operations are all about efficiency. They have found that pullets don’t need as much protein during the later stages of development as they do earlier. The general regimen is a fairly high-protein Starter the first month or so to help get them feathered out and off to a good start, then switch to a lower protein Grower for a couple of months to continue growing. Then around three months of age switch to an even lower protein feed. This slows body growth some and allows the skeleton and internal organs to mature a bit more to get ready to support egg laying.
There is another factor. How much protein they eat will influence when they start laying somewhat. They control when they start laying with both percent protein and lights. The commercial operations are not in a huge rush to get pullets laying as soon as possible. The first eggs are often weird in some way and are going to be small. There is not much of a market for those tiny pullet eggs. Remember that the pullets they use are the commercial hybrids that have a small body so they don’t need as much feed to maintain body weight and can more efficiently channel what they eat into egg production. Also, they are bred to lay large eggs. If small pullets lay large eggs they are more prone to laying problems like prolapse or internal laying. Also especially when they are just starting to lay a higher protein feed encourages then laying double yolked eggs or more than one egg a day. Since their shell gland normally makes just enough shell material for one egg a day, that second egg is often shell-less or very soft shelled. That can lead to breaking inside the hen and medical problems or if the egg breaks on their automatic egg gathering system it can make a mess. Teaching them to eat eggs when those eggs break isn’t a problem for them because of that automatic egg retrieval system.
In short, they’ve found that they are better off over the life of that laying hybrid hen by delaying the start of egg production to get larger eggs and fewer medical problems when they do start. They don’t need the more expensive higher-protein feed during their puberty so they don’t spend the extra money for it. They control that start of laying with both lighting and amount of protein they feed them.
Editted to add.
I just saw this is in the meat bird section. I don't have experience with them. What I wrote was talking about flocks that will be layers, not meat. Sorry!