It's not better for potential players for app to be paid, I'd have preferred it that way personally but that's because it simplifies a lot of things, but a few key things that a paid version of RISK would have issues with vs f2p;
- anyone that can't pay for it (either due to age or their country happens to be trade embargoed/restricted by america or no budget for games and so on) will just play free versions elsewhere
- lots of people are much more interested in trying before they buy for apps
- filling lobbies is pretty fast, it wouldn't be as a paid app
The app was released in 2015, so converting from F2P/P2P to paid app would instantly block 99% of existing players (including anyone that purchased premium for gems, or on another platform)
Having it as a paid app would mean cross platform would be much less valuable, might not even be worth maintaining some platforms as a result - and you'd have to buy it for each platform type (apple, android, steam) just to get what you already have on another device
A lot of games go for a subscription model instead, might seem nice having a $5 subscription for a month, but when you get premium it's permanent - you get to keep what you buy instead of just "borrow" it like a lot of games & streaming platforms
If it was a game released in 2020+ instead of 2015, it probably would've been a subscription (otherwise similar to now) or a paid app - without any "permanent remove ads/tokens/bunch of maps/cosmetics" - maybe would be more profitable too, but it'd be a big screw you to all of us that purchased it permanently to then force paid store access (losing platforms at minimum) or losing access to all purchases if not wanting to spend another x$ on it (and wouldn't blame anyone that would refuse it purely on principle there)