I think that the continuity of signature campaigns comes from gaining loyalty more than increasing the number of users, personally I used thechange and exch because of their presence in the forum which gave me assurances that they will not scam me for amounts less than $1000.
I also see it that way. Remember how ChipMixer was simply the number one mixer everyone used? They spent quite some money here, but I would say it paid off (for the time they were up running). If I needed a mixer, the first thing in my mind would be "ChipMixer", and their signature campaign was the main reason.