3) These extra fees go straight to the insurance fund, to protect against the fact that there is a much higher risk of insurance fund losses from highly leveraged positions.
However, BTC-PERP and ETH-PERP are more liquid, and so can handle the higher leverage.
4) In addition, FTX has been around for a year and a half and the insurance fund has been steadily growing.
https://ftx.com/status
We'll continue to revisit this in the future. Note that the high-leverage fees still apply to other markets.