Is there any way to remove and clean up all the junk data and why there is no policy made for developers to develop apps that after removal it should remove completely without leftover anything.
Hi there @rads091!
Don here from Shopify. :)
As you've experienced here, certain third-party apps being added to your theme will insert or require you to insert some code into your theme files in order to function.
If you don't wish to continue using a given app like this you would be well served to remove any code you would have needed to add in order to have that app function on your store.
As apps can't remove code after the fact from your theme code, it would be necessary for you to remove this code yourself if you wish to have your theme return to its previous state.
If you're having some difficulty with finding or removing the code added for a given app you can get support with this (and any other issue relating to the use of a third-party app in your store) by reaching out to the developers of any such app.
They will be able to help you by directing you to remove this code yourself or they may even be willing to help you to remove it themselves if you grant them limited access to your store.
If you have already removed the apps in question from your store you can search for them here in our app store to find their developers' contact details.
You are also free to revert changes made to .liquid files in your theme code if there is a time and date to which you want to roll-back.
All the best!