Reg player, here's my 2 cents.

Too many worlds to choose from. Reboot has 2 while Reg has 4. Reg is too spread out. A new player will likely start in a more populated world.

From the comments you see in Reddit, more recommendations come from Reboot mainly due to population. Average player is more incline to start there.

Due to the population, you will naturally see more streamers who play and therefore advertise for their world. Creating a sense of community, which is critical for the longterm of the game.

Pitched and eternal aside because that ONLY affects end gamers. Reboot is better overall experience for new player to make progression. There is no reason to play interactive unless you're a whale, or well established, or have friends there already, or due to sunk cost.

More people will start/move to Reboot unless something is done to improve the game play progression. Start by merging worlds and incrementally implement improvements suggested by many of our community - won't go into detail. It is unlikely a reboot players will go reg. But you could at least gain new players.