Unable to concatenate files with find ./subdir/* | sort | xargs -0 cat > merge.txt

Unable to concatenate files with find ./subdir/* | sort | xargs -0 cat > merge.txt

I am trying to concatenate thousands of files that result from processing the pieces output by split with
find ./subdir/* | sort | xargs -0 cat > full_merge.txt
The files under subdir are:
something.foo.aaaaa.output
something.foo.aaaab.output
something.foo.aaaac.output

...
But I get File name too long
Why?