Ethereum

This might be a dumb question but if most of the ETH gas fee is burned, why not just decrease the gas fees?

Is it really just to make ETH deflationary, at the expense of the cost to use the chain? Doesn’t that disincentivize usage?

the current gas limit is not set artificially low explicitly to burn more gas. The limit is based on what the core devs believe to be safe while preserving everyone's ability to run a full node on consumer grade hardware. We'll want to increase the gas limit and decrease costs as much as we possibly can while staying within the bounds of this constraint and the good news is it sounds like there are some large increases being planned for Fusaka!

Gas is fundamentally spam protection. It can only protect against spam if the cost exists. 

Decreasing that cost implies to enable more spam as an input to the system whereas burn is a neutral output for work executed.

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 🧭📉 . Ethereum Core Dev

Look at eip 1559.
Maybe @abdel could tell you more about the logic between base fees and burning.