In Heir To The Empire, Obi Wan appears to Luke for the last time with just such an explanation, having lingered too long already. Yoda and Anakin apparently never appeared to Luke again after the end of ROTJ.
But HTTE is shit as bad as TPM. Any explanation it gives on anything is automatically implausible and stupid because … because … ysalamiri.
I was simply pointing out that the idea Obi Wan can’t hang around forever to give Luke advice isn’t new.