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.
You are right, all have reason to hate the long-term campaign because after 2018 a lot of campaign that does not give satisfactory results. Of course this is increasingly making the bounty hunter to choose the campaign with a short duration to reduce the waste times so long.