Not only that, but 2017 has been probably a huge year for RMT-motivating content patches.
Fall 2016 got Bikers, Holiday 2016 got CEO Import/Export, last quarter got Stunt Circuits, and then this quarter got Gunrunning.
All those things combined, with a constant surge of new GTAO players -- and especially kids out of school and college for summer -- who suddenly all want MC clubhouses, drug businesses, CEO properties, luxury offices and apartments, yachts and supercars.
Then throw in the new Gunrunning bunkers and vehicles as a major summer patch.
And also that the game is constantly adding clothes, new real life inspired supercars (e.g. Bugatti Chiron; Aston Martin Valkyrie), and lots of ways to nickle and dime players.
So, for new players (or old/returning) players out of school for the summer, the game has a really massive amount of constantly new cool shit to buy.
If you're new to the game and you want even just a safehouse, property, and probably 1 business (e.g. clubhouse + weed farm) or office + warehouse, and you don't want waste 100 hours doing shitty missions to catch up to your friends, that's probably $20-30 USD to 'get into the game.' Throw in a nicer CEO office and maybe a combination of office/bunker/drug business, you're probably dropping $60-80 USD in GTAO cash, or at least buying one of the GTA5 + cash card bundles that bring the GTA5 sticker price back up to OG release full $60 retail or $70-80. If I had to guess I'd say quite a lot of new players that are planning to stick around with your friends at least grab a small cash card to skip all the boring shit and get into at least export/import or biker drug businesses....
and this quarter probably was their best yet because kids out for school want to get into GTAO but get right into export/import, crates, get a CEO office, biker drug business, AND now also the brand new gunrunning bunkers.
it'd be sort of like getting into vanilla WoW except the leveling is even worse/more boring, and being able to just $20 to skip it and instantly start raiding with your friends.