I'll give you the JW reasoning on this.
The further back you go, the closer to perfection mankind was. Like, God's Holy Spirit walked and talked and flowed thu the Garden of Eden, speaking with Adam.
Later, it was a burning bush, visions, dreams, and Angels like Gabriel sent as messengers.
Finally, Jesus and His Apostles. After they died off, that was about it. God then let His Word speak for him, and of what was to come later. Mankind is simply too far gone for Him to speak to on the levels he once did. The exception: The 144,000, and now solely the Governing Body via Holy Spirit.
Now, that's the JW belief system that I grew up on.
As an adult, I find myself asking as OP did. God could just solve all of this mystery and eliminate all false god's easily. Send Jesus to appear first in the sky, and simultaneously all throughout the world. Have Jesus do this every 75 years, every GENERATION. He could heal people, do miracles, etc. That would eliminate every other religion overnight, because if all other God's are FALSE god's, they won't show up. Wars over religion would end. Hell, world peace would probably break out, especially if he dropped some new tech to help grows, solve pollution (Cold Fusion), etc.
Then mankind would truly be able to start to move forward and the ones that choose to worship him, fine. The ones that don't? Fiery abyss for all I care.
It's such a simple solution.....but oh no! We gotta somehow sort thru a cryptic book written in the Iron Age by middle-eastern goat-herders, and THEN somehow pick the CORRECT denomination out of 250 Christian sects, or else you're toast. Lunacy.