The piecemeal approach ensures they avoid massive shocks and over-correction. The cure should not be worse than the disease.
There is also nothing to say they can't lower the funds rate should conditions warrant, as unlikely as that may be.
Perhaps a reminder to those who are younger - the past 10 years have been an aberration and not the norm when it comes to interest rates. The US and world economies have had long periods of growth with 10 year rates of 6% or higher. The current moves are as much about current inflation as they are cover for a Fed that has been looking for a way to end the mistake of ZIRP without actually saying it was a bad idea.