It’s extremely easy to obtain gold in Immortal. Spend points in the Treasure Hunter paragon tree, make it active, and go farm mobs open-world. The biggest limiting factor which causes players to be unable to upgrade the ranks of their gear is not gold, but the availability of scraps and dusts. That’s one of the things I addressed months ago…
I have over half a trillion gold in Diablo III. The reason is that there’s not a good sink for it (empowering GRs doesn’t easily put a dent in this much gold) whereas in Diablo Immortal there is, i.e. rank upgrades and gambling at the Antiquities NPC. The reason players don’t have huge amounts of gold is precisely because the sinks are good, and there’s literally nothing else to spend the gold on other than ranks / gambling for gear.