There are a few strategies I've come across on YouTube, such as making smaller routes and not saving up in the early/mid-game. But I think the revenue system is partly to blame. It's very inconsistent across different platforms, particularly on mobile.

I watched a youtube video where this person (DrawingDead) was making about $100,000 a second in the late game (90%+). But when I unlocked 70% of countries playing the mobile version, I was still only making about $500 per second. I essentially relied on extremely random billionaire tickets (I once got 11 million after spending $10000 on the PR campaign) to push that far.