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.