Been getting asked quite a bit why we're seeing fewer IMEI-based tracking methods, such as stingrays and tower dumps, compared to before, and why there are so many new companies entering this market with arguably less direct answers.
TL;DR:
Law enforcement has shifted to Advertiser ID tracking because it's asynchronous, and doesn't require warrants.
Stingrays and geofence warrants require being at a location to identify targets and establish probable cause on a large set of individuals. Warrants for major gatherings are not easy to obtain. Advertiser IDs allow you to buy someone's entire location history going back months or years from data brokers; there is no probable cause and no judge involved. This is because the data being purchased was not gathered for law enforcement but was considered a business good or OSINT. Carpenter v. US (2018) made warrants mandatory for pulling tower data from carriers.