So, they have to provide the same benefit to everyone, but, because a high earner can contribute more, they get a higher match.
Just tossing out numbers here:
A company provides a 200% match.
A person making 250K tosses in their 23,500, gets 47,000 from the company.
Their employee making 100,000 can't do that in many cases, but puts in 8% of their pre-tax salary, and gets 16,000.
Make 2.5x but receive a 3x benefit because they can afford the loss of pre-tax income.
It pays to be rich-ish.