To put it differently, the fewer pages you have, the more link equity flows through them. Increasing the number of pages simply dilutes that equity, thus making it harder to rank.
Don’t just take our word for it: Gary Illyes (Google’s webmaster trends analyst) stated in 2016 that an expansive site (one with numerous pages and deep directories) can actually be a negative for search engine optimization purposes if it’s not managed properly. He said:
“Narrow it down as much as you can. Don’t create low quality and no value add pages. It’s just not worth it because one thing is that we don’t necessarily want to index those pages. We think that it’s a waste of resources. The other thing is that you just won’t get quality traffic. If you don’t get quality traffic then why are you burning resources on it?”