When you sync in perforce, it updates the files you're not editing to the latest revision, and leaves the ones you're editing untouched. Git fetch, by contrast, updates everything that's changed.
Perforce's behaviour requires that client state cannot be expressed as a simple change number. Some files may be synced to change 5522, others to 5525. A git tree is always at a particular change, plus a local diff.
The cost of that simplicity is that git fetch ties p4 sync and p4 merge. If you want to pull unrelated changes into your tree and there are conflicts with your current work, then you have to deal with those conflicts immediately. p4 sync is low-risk, git fetch risks interrupting your train of thought with a merge.