Google has yet to say explicitly why they are making this move, but it's believed that it's a measure meant to stymie malware developers. Developers who can't update their apps were kindly asked to remove the apps from the Play Store themselves. They must also disclose on the app's Play Store page that they use this service by adding "This app uses Accessibility services" to its description.
On Android, these come under the umbrella of Accessibility Services, features that developers can take advantage of to help make their apps easier to use for those with disabilities.
Google main concern about abuse of the API is that it poses a potential security threat.
In an email (embedded below) sent out last week and shared on Reddit, Google told developers that it plans to remove all apps that utilize the Accessibility service from the official Play Store unless the Accessibility service is actually being used to power a feature for users with disabilities.
This is a very powerful feature, one that malware authors also noticed and incorporated into their malicious apps. Another option for devs who are using the API is to remove any requests for accessibility services within their app.
"All violations are tracked". Android will consider an app as inactive if the same has not been recently used in the foreground and the app package is not used by any other app package in the background.
If you've reviewed the policy and feel we may have been in error, please reach out to our policy support team. Then after a specified time, the feature will mark apps that haven't been used in a while as inactive, and will downgrade their size by removing the cache files.
As you can see, this change will most likely affect hundreds if not thousands of applications on the Play Store. Android has various Accessibility Services that can be used by the developers to improve their apps, but some apps like the LastPass have been using these services for creating a unique overlay on the UI and also control other apps.