There are many reasons imo for people to appear on these "celebrity" type programmes. Some to earn money, some to try and boost a career which is flagging, some who are media celebrities and whose "fame" is based on notoriety rather than any talent. Then there are shows like Masterchef or Popstar to Opera Star, where some want to be tested and to learn.
Meat has explained why he has appeared on the two he did. Being a judge on Popstar to Operastar made good business sense when he wanted to be based in Europe to promote HCTB; the money he earned from competing in Celebrity Apprentice was for a wonderful charity, plus he saw it as an opportunity to learn; and both would have provided networking opportunities. Neither were done primarily to garner publicity, even if some was generated, and as he says, any you get is fairly shortlived. To me his choices have been shrewd.
I'd agree that many who appear on this type of programme do so for reasons open to criticism, but imo both of Meat's choices have been for good and sound reasons. I get the sense that his appearance on Ghost Hunter was done mainly out of interest and for enjoyment
Caryl