The Ethereum network is imploding under its own weight. Running an ethereum node has become quite expensive and requires very state of the art hardware just to keep up. There’s a reason bitcoin chose the constants it did.
Note that with the "fast" mode you still have all the blocks, and with that all the information needed to recreate the state at a certain block somewhere in the past. And you can still help the network by syncing those blocks to newly spawned archive or fast nodes. It's just that requesting the state (e.g. balance) at a certain block in the past takes some computational work. Most people are not interested in that however, which is why it's the default synchronization mode.
[0] https://etherscan.io/chart/chaindatasizefull vs https://etherscan.io/chart2/chaindatasizefast