Yes, that it was especially rural environments and not having much options otherwise to live around while building.

Sauna that was built then wasn't just one hot room, but it also had at minimum small changing room dressing/undressing, relaxing between turns in steam room. Also if it was first building made then adding also lounge which served as living space with beds and cooking stove while building house was common. With sauna you had place to stay warm first winter, able to get warm water, wash clothes, yourselves and even a give birth old times. Building sauna first made lot of sense.

These days sauna for home builders is more about getting sauna somewhere in that floorplan where works well for the intended users of that house.

>sauna is often built first because it serves as a place to live while you're building the house

wouldn't a kitchen accomplish that goal better?

Due to lack of running water in those times (and still in many cottages) cooking is done above a fire, water is brought from the lake. A kitchen won't serve you well if you're just trying to get through a long winter of -30c.

The sauna provides heating.

Average yearly temperature in Finland is reported as 6.5 Celsius