Because from this view, you _ can_ have such things as 2.75 people because that “2.75 people” is not just a ratio of a total population of similarly counted objects BUT ALSO CAN BE a ratio of contained parts.
So, If 2 people contain 2,000,000 parts, 2.75 people contains 2,750,000 parts.
This also allows you to round up and down as needed because now you’re rounding parts ratios. With that in mind, you can either take take a 250,000 parts from another grouping called a “person” to make 3,000,000 parts or “3 people”, or you can put aside 750,000 parts and add it to a 250,000 parts from other. Or you can combine in other ways as needed. It’s not that you can’t do it with the “decimal people”: