where MC doesn't know his identity
Back when I read more random cultivation novels where the MC eventually discovers they had better origins than some random orphan in a cheap and backwater town or whatever, I came up with a pretty solid 'reason' as far as I'm concerned.
We usually see the whole 'young master' trope, usually the fodder to be slapped down or whatever, but it stands that the MC would be in that exact situation if they had their original backstory.
So there is a 'rule of non-interference' where some powerful factions who can afford it, send their young to fend for themselves alone in another location, instead of being given everything their families can provide. That turns an MC with a powerful backstory, into an MC who also had to struggle for a while to strengthen their mind and soul.
Being brought up 'by your backing' in a cultivation novel almost always seems to be a flaw for cultivation, as you rarely exceed the struggles that your family allows you to make in a safe space, while MCs who have that powerful start but no backing are 'against the world' and grow for it.
You can justify any number of remote monitoring, soul flames, viewing fate and other things, but in the end controlled struggle; while having some memories temporarily suppressed as a coming of age thing doesn't seem like an unreasonable 'challenge' for someone who is being tested as a heir to a major force.