2. Preferred company or service that they do like to advertise
I think this rarely happens. Most advertisers on Bitcointalk have always been crypto casinos, and if they pay good, people will apply. One exception is if it's a scam casino with a history of defrauding its clients. A perfect example is 1xBit that never attracted respected individuals even if they paid decent amounts.
A more common reason for a switch between two almost identical campaigns could be different campaign managers. Maybe I had a better experience when I was in the campaigns run by Manager A than B. Some rules aren't always as strict for all posters if the campaign manager likes you and the quality you bring to the project.