It is all about centralization vs. decentralization.
For blockchain platforms, the scalability of a given chain often boils down to the level of decentralization possessed by the network. Highly decentralized ecosystems (such as Bitcoin) are quite slow, whereas networks that are more centralized (like EOS, with its 21 Block Producers) are much faster.
Therefore, having fewer nodes producing blocks generally makes things faster. However, centralization reduces the interesting properties that blockchains innately possess — namely their resistance to censorship, transparency and overall immutability.