When internet bandwidth became sufficient to pass enough data fast enough to satisfy gamers' appetites, some egg-head marketers realized they could sell half-assed and unfinished content as "early access" to the gaming community on the premise that said game content would eventually be fleshed out, iterated upon, and polished. This also allowed them to fire (or not hire temp) beta testers because the gamers became the beta testers.
Soon(tm) never happened because the content was already released. On to the next "feature"!
This is not limited to any one game company. But many companies that relied on this production method either failed outright, or seeing their peers collapsing under the weight of their piss-poor coding, bad practices, and lack of customer support, realized that a storm was coming and finally made good on their promises.
In Riot's case, they have a product that is generally fun (when you do not consider the toxic players), has a great deal of nuance, requires skill, and has no end-point. Its a recipe for continued success so long as the product features are properly iterated upon and tested.
Personally, I've sent Riot enough money to equal the purchase of any decent game at today's market prices. And I've only every bought a few skins and rune pages. All my champs have been bought with IP.
If it helps Riot to know, it was the Get Jinxed video that got me playing and paying. Saw some folks on the Zulu squad forums had changed their avatars to Jinx gifs and said "WTF holy crap that is awesome! Where get?"