A friend asked about ulterior motives in going back David Tennant for a special in Doctor Who. Here's my answer:
It's the "special episode" of ER where Cloony returned.
It's the wrestling show that books Logan Paul in a big match.
It's brining Spock back in Search for Spock
It's the local restaurant that hangs a "Under New Management" banner when they replace the General Manager.
It's bringing Sarah Jane back in School Reunion.
It's an attempt to get a look-in audience of lapsed fans. It's an attempt to generate buzz. It's a ratings grab. It's business.