I did say that I took a glance at google search. This is not a academic paper with careful study with tight citations from the last 100 years. If you want that, go and do the work yourself.

Here is a few new random google glances: https://venturebeat.com/2017/11/28/newzoo-game-industry-grow... $116 billion in total video game market, $50 billion for just the mobile market. How much of that is micro transaction? Don't know. How much is loot boxes. Don't know.

Blizzard reported more than half their revenue, $4 billion, was from micro-transactions. https://www.gamespot.com/articles/activision-blizzard-made-4...

EA reported similar $2 billion, almost half of their revenue, from micro-transactions. https://www.tweaktown.com/news/57475/ea-earns-1-68-billion-m...

According to this random article, loot boxes are around $30 billion this year and expected to reach $50 billions in 4 years. https://www.gamesindustry.biz/articles/2018-04-17-loot-boxes...)