Why do you think Goku decided to leave in less than 1 year?

[Seekeroftruth]

Goku spent less than 1 year on Yardrat and learnt to transform into a SSJ at will, train a bit and, picked up a new fashion sense and learnt the instant transmission technique. However, as we saw in Super that there were several techniques that Son Goku could have learned such as the spirit fission if he had stayed on the planet longer. What do you think prompted Son Goku to leave the planet so soon? Do you think it could have possibly been due to Frieza heading to earth and Goku sensing it possibly being endangered?

[Lionel]

I think it's more or less confirmed that Freeza's survival and imminent invasion of Earth is what made Goku hastily finish his training on Yardrat -- he was looking back on his show of clemency to Freeza on Namek and regretting having done so as he was talking to Trunks.

[dario03]

I've always wondered why nobody went there after Goku came back (until Super). All most of them do is train anyways. Goku could IT himself and some others there whenever couldn't he? I know he says they aren't that strong but some probably have a power he could lock onto and if not King Kai could help him. With IT he could even have taken Gohan and Piccolo there but came back every night so ChiChi wouldn't get so mad.

Did they cover why this didn't happen in Super?

[Peach]

Because Goku learned everything that the Yard Rats had to offer.

You need to look at that story in the context of Dragon Ball Z and not all this other stuff invented two decades later by an author who forgot much of his own source material.

Goku also cared about resting. He exited the time chamber 3 months early in the Cell saga. He trained in lower gravity than Vegeta. He saw significantly higher gains because he gave his body chances to rest. I think he'd want to rest after training so intensely with the Yard Rats.