I don't think it's something the show does on purpose. The actors probably choose to pursue other opportunities because the money is not enough to stay around for.

@Stratego! said:

I don't think it's something the show does on purpose. The actors probably choose to pursue other opportunities because the money is not enough to stay around for.

So they create a show about an officer and his sidekick solving crime and only pay enough for one of them to stick around from season to season??? Also it must have been very popular since there are so many seasons. This being the case it would only make sense to pay both actors enough to stick around.

Well, consider the raise the actors probably get with every contract renewal. And that the actor playing the officer gets a higher salary because he has a bigger role and is better known and more established. It seems very likely that the producers feel it isn't worth hanging onto yet another sidekick at any cost.

@lantzn said:

Why did this show have so many sidekicks? As much as we enjoyed it, it was annoying they didn't bother in most cases to let you know why they left. I've never seen a show do this so often, it feels like a running joke.

When it comes to "departures" while a show is still going strong, I think the answer (usually) boils down to three likely possibilities:

(1) Now that they are part of a hit series, the person thinks they are worth more than TPTB are willing to pay. Talks breakdown...person walks, OR gets tossed out on their kiester for being a money-grubbing ingrate who has forgotten they were a “nobody” before the show took-them-in.

(2) The person has a " on their back"…sex?/drugs?/alcohol?/gambling?/mental breakdown/etc. Reliability becomes an issue. So TPTB, instead of about the possibility of scandals and lawsuits; cut-their-losses.

(3)Someone made them an offer they can't refuse. The person is offered and the lead in their own series and/or a movie deal; so they cut and run.

(4) Any combination of the Above.

(5) All The Above.