According to the support document, Adobe says that the reason behind the removal of the apps is because most of the features has since been brought over to its Fresco app. “Everything you love in Photoshop Sketch and Illustrator Draw has been combined and more in Adobe Fresco. If you’re using Photoshop Sketch and Illustrator Draw, Adobe encourages you to enjoy the powerful, comprehensive drawing and painting tools inside Adobe Fresco.”
This means that instead of having to maintain multiple apps that share similar functionality, users can just move over to Fresco instead. The app will be removed from the App Store and Play Store on the 19th of July, but users are free to continue using it. The app will officially no longer be supported on the 10th of January, 2022, but you probably can keep using it after that as long as it works.
In the meantime, those who are interested can download Adobe Fresco for free from their respective app stores, but there are also additional premium features that can be unlocked for $9.99.