This can naturally lead to lower average "distances" between proposals. In a simplistic example, lets assume 100 proposals existed in the "good old times" and they were different at random. Let's further assume in the "bad new days" people use those old ideas, change/improve upon them just slightly ("add noise"), but some old ideas are less often picked up than others. Say for example the least attractive old proposal is picked up twice, whereas the most attractive old idea is picked up and changed in 100 new proposals. Then, there is a lower average distance between proposals, all the while the total range of ideas has increased.
Because it's Friday and I am waiting for my oven to finish cooking my food, I wrote a small simulation. It's probably full of mistakes and I may have made terrible mistakes in my assumptions, but I thought it's fun: