Because people are in different situation. Lucky for you, you didn't need that stimulus as much as others that you can invest it somewhere else. But to the rest of the beneficiaries who have lost jobs, business, apartments, and whatnots due to the pandemic will have no other choice but to spend that free money on more basic stuff.

But in terms of putting money into Bitcoin, it shouldn't just be your stimulus. It should include a portion of your savings, salary, income from other sources, and so on.