Two reasons for that:

1) These are the first year income tax cuts, but most of these income tax cuts are getting phased out over time after the first year. By 2027 some of these income groups may see tax increases, and most won't see much benefit at all.

2) The temporary income tax cuts are peanuts compared to what is happening with the corporate rate, pass-throughs, capital gains, and estate tax (all permanent), which benefit people that own companies and/or inherit wealth - which is predominately the richest people. The richest people in the country don't get their wealth from their income, but rather from returns on capital.

That's because this only looks at income tax.

The tax bill is a boon for billionaires because of (1) estate tax repeal (house) and (2) corporate tax cuts that will benefit the capital class that holds corporate equity.

This shows only a small portion of the impact of the bill - the SALT and child/marriage/standard deductions increase for earned income, but none of the passthrough changes, changes to the way unearned income (stock market investing, e.g.) is taxed, corporate changes. M/Billionaires don't file a 1040-ez, but that's what this page is showing (before said deduction increases expire)