Their previous arena (Sioux Falls Arena) was very outdated, built in the 50s. They were in desperate need of a new home for the Stampede as well as a place to host other events like concerts, monster jam, etc. Additionally, Sioux Falls is growing like a weed, with population doubling since the 90s.
Hockey in general is also booming in the city; They got Scheels IcePlex, west of the airport, with 3 sheets, and the new rink for Augustana (Midco Arena) etc.