Originally Posted by MikeDVB
It's more than just the migration itself. Let's say you're a Plesk host and your clients are used to Plesk and all of your documentation is written for Plesk. Furthermore your staff are familiar with and trained on the usage of Plesk.
There's a lot more to it than simply making the change. Re-tooling your documentation, re-training your staff, and then helping your customers understand the changes/differences and how to make use of a totally new control panel for which they may or may not have any familiarity at all.
So yes I am sure there are those running Plesk on Linux that are migrating to cPanel - but I am sure there are a lot of providers that it's not so simple a task to completely change their underlying control panel.
That's life, if a business cannot be ready to make changes then they cannot withstand the ever changing climate of the industry.