Complex sentence: The arena was built as a new home for the Lightning, necessary because of the lack of another suitable facility, as both the Bayfront Arena in St. Petersburg and the Expo Hall at the Florida State Fairgrounds were too small for an NHL team.
Split into simpler sentences: The arena was built as a new home for the Lightning, necessary because of the lack of a major league-sized arena in the Tampa Bay Area. The two existing arenas in the region, Bayfront Arena in St. Petersburg and the Expo Hall at the Florida State Fairgrounds were too small for an NHL team.