Why was RIOT made?
Let's see...
Battle Royale games are the hot thing right now. As a game developer you want to get into what's hot. The problem is, games take years to develop. If you start a game that takes 3 years to get to market you run the risk of the BR craze being over and you fail to make the big profits you were hoping for.
Or, you find a game that's already out and mature, buy it, develop your BR mode and hope to God that you can expand your playerbase. People who like the old stuff will stick around, because you're not removing the old stuff, but you're really hoping for lots of new players who are going to want to drop a lot of money.
TL:DR, the whole reason LO bought APB was to get a BR game to market quickly and at a reduced cost.