Like many current decks in Modern, Temur Rhinos is a deck that began with the printing of Modern Horizons 2, particularly because of Shardless Agent and Fire // Ice. Prior to Shardless Agent entering the format, you had to play Ardent Plea or Demonic Dread in order to have eight cascade spells. Each had their problems. Plea requires you to be four colors and Dread requires there to be a creature in play to cast it. Shardless solved both of these problems for you.
MH2 also gave you Fire // Ice. It might not look like much, but it gave this sort of strategy a critical amount of interactive spells that work with the deck building restrictions of a cascade deck. Between split cards, the Modern Horizons 1 and 2 pitch spell cycle and Adventure creatures, you can play a normal game plan without sacrificing too much efficiency.
Initially, Rhinos was one of the more popular strategies initially after the release of Modern Horizons 2. In fact, it won the first major event after the release, the season 1 MOCS Showcase, in the hands of Yuuki Ichikawa.