Like most popularized MOBAs that have come out since DotA, (mainly LoL before Smite) the barrier to entry is very small and the game is easy to learn, however the more you learn the more you realize how complex MOBA mechanics are and you realize how bad at them you are. I.E. skillshots, last hitting, map awareness. Smite is an easy game to play but difficult to truly be good at so it draws in a large player base. Also, like LoL before it, most of the core gods/champions are variations of DotA champions or they combine mechanics of two familiar champions from DotA. Smite has recently started coming out with champions with unique mechanics which I think is great for them.