Kittens who cry when left alone will usually not stop crying until after they're 2 years old and some kittens may never fully quit crying when you leave them alone.
Your cat probably only cries for awhile when you're leaving them alone and then stops after you've gone.
Just like a kid will cry when their parents leave them with another parent or with someone else.
The kid eventually stops crying after the parent leaves.
You could get your kitten a second kitten so it will not be lonely when you do leave them alone and that can stop the kitten from crying when left alone.
It's usually recommended to get cats and kittens in pairs so they'll have another feline friend to play with.