My understanding of the technical details behind the Economic Impact Payment is that it is, to a certain extent, means-tested. The feds look at your 2019 tax return and dump money into your lap via either check or whatever direct deposit method you listed on said tax return. If you haven't yet filed taxes for 2019 they look at your 2018 return; if you didn't file 2018 taxes either the IRS has set up a portal where you can enter your information and grab your money. The payment isn't subject to federal garnishment either, unlike what they do if you're behind on past taxes or student loans and they just seize your tax refund to cover the delinquent balance.
The amount you get as a single filer is $1,200, unless the adjusted gross income on the tax return that they pulled information from is above $75,000. Then the payment starts to go down little by little, hitting zero if your adjusted gross income is $99,000 or higher. This is called a phaseout and they're everywhere in federal tax, at varying AGI levels for different tax deductions and credits; the IRS does this to prevent situations where your total tax bill is $5,000 at $49,999 of income but your taxes jump to $10,000 if you get paid an extra dollar. That's gay and it only happens to particularly poorly-implemented shit like the income-based discounts (actually advance payments of a tax credit) on health insurance premiums paid through an Obamacare marketplace.
So if you check your bank statement and your Economic Impact Payment is only $600 or something, that's why. But there's another catch, too. The Economic Impact Payment isn't no-strings-attached free money; in technical terms it's "an advance payment of a new refundable tax credit that you're expected to qualify for on your 2020 return." If your total income for 2020 winds up being substantially higher than the amount that the cash airdrop was calculated based on, you might wind up owing back some or all of the dosh you've just received. If your total 2020 income is substantially lower -- such as if your ass got furloughed and your unemployment benefits suck -- then you might get the remaining portion of that free government money when you go to file your 2020 taxes in a year.
tl;dr it's loosely means-tested but it's still means-tested. There was a lot of debate over whether to only give the money to people earning less than a specific threshold vs. whether to give the money to everybody and claw it back later. The implementation of the payment appears to have been a compromise, as is absolutely fucking everything that the Fed does.