Because they are tightly linked for most people.
I've managed to increase my income ~5x from what it was when I started but to do that I have had to put in 2 hours/day of side study.
The 99th percentile ("top 1%") of wealth by household seems to have been be $8.4M in 2007, according to https://economix.blogs.nytimes.com/2012/01/17/measuring-the-..., the most recent calculation I could find from a quick Google before heading to work - I'd love to see these calculations done with the raw data at https://www.federalreserve.gov/econres/scfindex.htm . From the summary on that page, they surveyed some 116 million households in 2007.
Suppose you tax all holdings at the top 1% of wealth by 1%/year, which is significant but not enough to wipe you out - after 50 years that leaves you with 60% of your original savings, assuming you weren't investing it.
That yields as a minimum $97T in tax revenue per year ($8.4M * 1.16M * 1%), and almost certainly significantly more because there-s a short tail of people with much more than $8.4M net worth. But if you split even this much among the 5% of households with "very low food security", that's $16,800/year. That's a lot of food.
(An actual scheme would have some sort of progressive tax, also, not a discontinuity at a certain dollar value)
Total US GDP for 2016 was ~$18T.
It seems a bit unrealistic to me to think we can get 5x GDP in tax revenue each year.
So what is the catch?
Hold up -
1. Why is this about working more hours, instead of working harder / more effectively? There are 168 hours in a week; even if you don't sleep, you cannot maximize your income beyond about 4x just by working more. I am currently making about 15x the lowest hourly rate I ever worked for, and I'm still fairly early in my career and feel like there's a lot of room for my salary to increase as I become more skilled.
2. I'm reading the discussion was about a tax on wealth, not a tax on income (dwealth/dt). If you're making a decent living and want to make more money so you can spend it on things that are not investments (consumer goods like video games, services like vacation travel/hotels, charity, raising more children, sending them to college), a tax on wealth will not affect you, because your wealth stays right where it is. And doing all that is net-positive for the economy.
'majormajor is clearly talking about wealth in the sense of static assets, not change in assets over time: I'm worried about having a single medical emergency, not having one every year. Make enough for your (static) safety net, then stop making more money.