Went through a similar experience with our own Slack app. We had created a fairly popular app called "Export" for exporting channels from Slack in a variety of formats. It was an approved Slack app for several years before being summarily expunged from the directory when Slack changed their terms of service.

Surprisingly, not being listed in the Slack App Directory is not a death sentence. It just means you have to invest in alternate discovery channels.

Speaking of, the link for Slack Export is:

https://export.fountstudio.com/