You can't really blame bounty hunters for hating long term campaigns, of course in 2017, everyone is on the boat of the hype, so it doesn't matter if the campaign is long enough. I've seen Legendary members that time raking up thousands of dollars in a campaign that lasted months and months.
But 2018-2019 was different though, many project fails and those who survived just got a measly payment. You are lucky that you have earn on Airwallet. So it's a case to case basis, but I'm sure majority was complaining because they didn't get the money that they were supposedly promised by many project.
Truly i am agree regarding long term bounties which 6 months, Anyone can not blame long term projects promoters. After 2017 a few long term campaigns reached big fund and paid rewards on time. Currently i saw a campaign here a lot of high ranked members joined from first week and till now 22 weeks and provably these is last week. They will get expected rewards hopefully.