the real reason that it took multiple years for Obi-Wan's ghost to direct Luke to Dagobah for further training with Yoda was that Yoda failed to actually tell Obi-Wan where he was planning to go into hiding when they parted at the end of RotS, so Obi-Wan had to spend about a year tracking Yoda down in the Force so he could ask, and then convince Yoda to actually tell him what planet he's on
this takes a while, because it turns out that Yoda is reluctant to admit that he doesn't actually know the name of the planet he's hiding on, because he let the Force guide him to a suitable place for his exile and didn't think to double check the coordinates he entered
once Obi-Wan gets over the impulse to tear out his ghostly hair, he resolves to just check the navigational computer in Yoda's ship to find the coordinates
unfortunately, Yoda admits that he sank the ship he arrived on in the swamp a month after he landed and built his hut
Obi-Wan decides that that's fine actually, since he's a Force ghost and no longer needs to breath and can just go down to the ship to check the logs regardless of its current location
except that the ship has been submerged in the swamp for about 20 years at this point, and the ship has no power, and the computer has been totally waterlogged
at this point, Obi-Wan spends another entire year so furiously frustrated that he is unable to marshal the focus needed to manifest as a Force Ghost at all
once he finally calms down, he spots and identifies a unique subspecies of worm that lives in the swamp, and is able to use the power of his lifelong special interest in worms to instantly determine what planet they're on
he resolves never to tell Luke about any of this, instead insisting that Luke simply wasn't ready yet before he made contact during the battle on Hoth
(it's worth noting that Qui-Gon knew they were on Dagobah the entire time, but didn't speak up because he thought it was funny he was confident that his Padawan would figure it out eventually on his own)
