Lock-free compaction. Why not?

So anyways I talked last week about lock-free vacuum. Since then I almost
finished creating a plugin that works on all Jetbrains products. It hooks
to the internal database tool and displays the internals of the database
and some stats. I would use this for my next phase: autovacuum with
compaction.
The thing is, after reading the code a million times, I still don't
understand why lock-free (or minimum locking) is such a big problem! Is it
that hard to lazily move tuples from one page to the other after
defragmenting it lazily?
I even made (a super simple equation) to calculate how much disk space can
be reclaimed, and created a full list of the advantages including
maintaining clustered indexes. This would of course be followed by
benchmarks.
Here is the wip plugin btw
https://github.com/ahmedyarub/database_internals_plugin/tree/2.0.0 which
should be released this week.
Like I don't even trust ChatGPT at all but I kept on trying to find reasons
for not doing it but I couldn't find any!
Such a trivial change that can bring a huge advantage. I just hope that
somebody could find me a reason for why it wouldn't work.

Really appreciate your patience,
Ahmed