Summoner Spell Req

I think its riots way of getting new players to try each summoner spell

Riot talked about this when they changed the level requirements for pre-season, pretty much new players won't properly understand the game's mechanical uses it between their own spells and their champion's just yet. So Riot gives easy spells that are just press once and you use it (like Heal and Ghost) so they don't need to fully think about more in-depth while learning the basics. Meanwhile spells like Flash and Smite are more in-depth spells with their uses. Sure Flash is just a blink, but new players won't fully comprehend all of its diverse uses as a level 1. In addition with Smite won't understand it's proper place in the game yet as a non-champion damage spell (they won't know of jungle items yet, which this also stops new players from buying as laners as a result).

So while a smurf would want every spell at level 1, the game doesn't cater to them at these early stages, it caters to keeping things basic for actual new players to grasp one thing at a time.