Database not cleaned after delete your plugin

Dear Team Support,
I would like to know why your plugins don't delete their data from the database when we uninstall them and delete them?
As I read many times, good plugins should also remove their database when uninstalled and deleted as unnecessary database is not recommended because they slow down the site and can create bugs and as WPMU is a paid membership, I am expressing here my surprise and my disappointment and I really wish to read your good explanation about that.
Thanks in advance,
Momo