I'm not entirely sure that the cost is exponential as the parent stated, but it certainly is superlinear above a certain threshold in my experience.

There are a few issues you have to deal with. The first is how adoption happens. This is generally based on power structures and reputation. If you are in a position to mandate a change, the cost is potentially lower (see below, though), but if you are not then you have to influence enough people to make a change.

There are many ways to do this, but I will split it into 2 for simplicity. First, you can try to influence the rest of the group directly. As the group size grows, this becomes progressively more difficult because your message is lost in the noise of other people pressing their own agendas. Once you get above certain point (say about 8-10 people), your odds of success drops to near zero.

The other main way is to pilot a project and use its success to influence others. Setting up the pilot requires influencing a smaller group and therefore you have higher chances of success. The problem is that when you pilot a new way of doing things, you are intentionally breaking consensus. You now have a small group of individuals who have experience that nobody else in the group has. Whether the adoption of the new technique is successful or not, this leads to increased cost as attitudes change.

The bigger the group, growing out a pilot into a larger project becomes more expensive. This is essentially the same problem as before -- you may be in a position now to mandate a way of working, but if you are not, then you have to create another round of pilots to move the idea around the group. But now you have another problem -- the implementors of the new pilots are different than the implementors of the original pilot. So you will now have more than one message coming out. You now have to harmonise that message in order to drive adoption.

At every step, there is a chance of failure (sometimes quite high). The chance of failure grows as size of the group increases, because the external pressures to not change are higher. Again, there are several possible outcomes, but I will pick 2 for simplicity. You may find that your idea is rejected. You have now spent resources on your pilot that you will have to reimplement in another way. Another outcome is that your adoption is simply stalled -- you split your group permanently. This has cost implications ranging from staffing, to training, to tooling, to management, etc.

Now, assuming you don't fail, you may have organically grown the adoption in your group (which is ideal), but as your group size grows, the possibility of that decreases (because the risk of failure increases based on the size of the group). More likely is that you have gotten enough reputation to be able to mandate a change.

Mandating changes has costs as well. The first is that some people will be uncomfortable with the change and will quit. You now have to replace those individuals - which costs you both lost productivity, referral fees, and training costs. This is more likely as the group size increases because you are more likely to have diverse, strongly held opinions.

The next biggest cost would appear to be training, retooling, etc. However, there is a hidden cost -- compliance. Very good people who dislike the change will leave. Very poor people will not leave -- they will simply refuse to follow the new strategy competently. This may be because they are depressed over the change, scared of how the change affects their influence, and many other things. These people can often end up sabotaging your projects (mostly unintentionally, but as they are usually quite upset they also don't care if they do). As the size of the group increases, the chances of building an unshiftable group of discontents grows.

If you want to make a lot of money, become a consultant introducing new development techniques into large organisations like banks. It's a bit like siphoning all their operating capital into your pocket because you have no hope of success and can blame all your failure on other people.