If by metric style, you mean utilizing metric prefixes, it's simply because few people ever needed times as short as fractions of a second before then. Our larger units of time are very old and were already well established by the time people created the metric system, but instruments precise enough to measure anything under a second were pretty new. Essentially, we didn't have something already in place for smaller units of time, so new units (or rather fractions of a preexisting unit) were created with things like ease of calculation in mind.