They use interest rates to protect against inflationary (and deflationary) spirals, which are known to be devastating. The effect on the unemployment rate is a known, and predictable, side effect. But formal unemployment is small compared to labour force dropout anyway, and the latter is not necessarily so sensitive to economic conditions anyway. Besides which, the unemployment rate can't really keep going down forever.

Zoom out; recent levels are actually quite impressive in the USA. Yes, they've climbed since 2023, but they're only just reaching the pre-GFC minimum (https://www.bls.gov/charts/employment-situation/civilian-une...).

Zoom out further: https://fred.stlouisfed.org/series/UNRATE/

Had it not been for COVID you'd be at more than 16 years without a(n NBER-determined) recession, long enough to suggest a fundamental shift vs. how things worked in the several decades before that.