Yeah, it probably is too low. On the other hand, at least those campaigns have a merit requirement--there's no obligation for a manager to require a particular number of merits, and it's a good thing when they do.
Merit requirement is sometimes good, but it should not be the sole criterion for campaign managers - some members
earn merits only by using their alt accounts of by buying them. Quality posts usually entails merits, so it is not difficult to choose between good and bad members. What we can all see is a very small number of members who are ranking up thanks to some contributions to the forum, which is a problem when some good signature campaign is show up - there simply aren't enough qualified members.
...which indicates that there is some sort of personal preference , 5 people might think your posts deserve to be merited while 10 other people might think your posts are complete trash , some people do post quality posts but members hate them for their shitty attitude - thus they earn way less merit than other members with the same post quality.
I totally agree with your opinion, for those who are active on a daily basis on forum it's not hard to notice that some members have their favorites when it comes to merit, and some members always get merited, others never or on rare occasions. Personal preference is very important factor in merit system, so it's not all about writing quality posts. Some members have even publicly admitted that that they got 50 merits for single post, even if that post was not some super extra quality content.