AppCache was standardized in the Offline Web applications section of the HTML specification. The standard is formally referred to as application caches. New Web applications should be built around Service Workers. Existing applications that use AppCache should migrate to Service Workers. AppCache access was removed from insecure origins in M70. This intent addresses AppCache usage in secure origins.
First and foremost, AppCache is a deprecated standard with serious architectural concerns. Second, Chrome's AppCache implementation is a security and stability liability. AppCache is documented as deprecated and under removal in MDN and in the WHATWG standard, and marked as obsolete in W3C’s HTML 5.1. It is incompatible with CORS, making it unfriendly for usage with CDNs. Overall, AppCache was changed in over 400 Chromium CLs in 2018-2019. It has imposed a tax on all of Chrome’s significant architectural efforts: Mojofication, Onion Souping, and the Network Service. The security benefits of the removal are covered under Security Risks.