If I can get $20k a month with one of the safest investments around

8% Treasuries don’t exist. The current treasury rate is closer to 4.5% during a period of 2.5% inflation. Higher treasury rates tend to be paired with higher Fed Reserve rates, which tend to occur during periods of high inflation. So the hypothetical 8% Treasury will only be available during periods of 5%+ inflation anyway. You’re still only netting real gains of 2-3%.

Its a safe hedge against a downturn when you only care about preserving your liquidity. It’s a real risk when you consider the possibility of a bull run. You’re effectively losing money when equities surge while you’re setting on a cash-convertible.