Late Gen-X/Early Millennial here; there was a time before the consolidation of radio stations and invasion of iHeartMedia (at the time named Clear Channel) where DJs had the final word in what got played and most were quite good at introducing new music. Here's my experience form the outside of the industry: once consolidation started there was a push to use canned (pre-recorded) intros, outros, and interstitial announcements to reduce costs. Stations often kept some talk shows, but few kept real DJs. This let stations use a small number of voice actors for a large number of stations. Combined with centrally controlled playlists they were able to push the costs down and increase profits to the point that older style stations with bespoke DJs couldn't compete financially and either adopted the same model or they sold out.

EDIT: I may be misremembering, but there used to be a limit on how many stations a company could own in a given market.