There must be a limit to how much data is transferred across the bitcoin network in order to keep the ability to run and use your own node accessible. A node is required to interact with the global bitcoin network - if you do not use your own node then you must trust someone else's node. If nodes become inaccessible to run then the network will centralize around the remaining entities that operate them - threatening the censorship resistance at the core of bitcoin's value prop.

The bitcoin protocol uses two main mechanisms to keep node operation costs low - a limit on the amount of data in each block and a robust dynamic transaction fee market.