WWI is more understandable to me, as war was seen more as a jolly good time then the horrid sufferfest it turned out to be

Your question is really founded on a false premise, as it implies that everyone went off to war at the beginning of WWI in a state of 'war enthusiasm', an assumption that has been heavily challenged by social historians in the past 30 years.

In WWI, as in WWII, most of the combatants began the war with conscription; although you had some volunteers, who enlisted for a variety of reasons, most men save for perhaps Britain 1914-16 and the United States 1917-18 had no choice. Once their 'number came up', they were drafted.

I would encourage you to watch these two lectures, one shorter than the other, by Michael Neiberg and Catriona Pennell, both of which examine why people chose to enlist at the beginning of WWI. It was more out of a spirit of 'defend the fatherland' than 'GOLLY GEE, WAR!!!':

https://www.youtube.com/watch?v=iMBD71SB10E

https://www.youtube.com/watch?v=5W0657Bwn_A

I've also given these answers in the past, which should help:

• [Diplomatically, why did WWI last so long?] (https://www.reddit.com/r/AskHistorians/comments/2yp7xj/from_a_diplomatic_standpoint_why_did_ww1_last_so/)
• [What did the average soldier of the Triple Entente know about the reasons the Great Powers went to war in 1914?] (http://www.reddit.com/r/AskHistorians/comments/35ykqy/how_much_did_the_average_soldier_in_the_triple/)
• [When the trench stalemate set in, why did the Great Powers not make peace?] (http://www.reddit.com/r/AskHistorians/comments/36br6e/when_world_war_i_stagnated_into_trench_warfare_in/)
• [Did a lack of open press facilitate errors and mass death in WWI?] (http://www.reddit.com/r/AskHistorians/comments/39xp50/today_it_seems_as_if_every_military_decision/)
• [Were civilians aware of the military situation/details in WWI?] (https://www.reddit.com/r/AskHistorians/comments/3dudse/were_citizens_aware_of_the_military/)
• [What was the public reaction to casualties on the Western Front?] (https://www.reddit.com/r/AskHistorians/comments/3e1mr0/what_was_the_public_reaction_during_the_first/)
• [WWI v WWII: Trauma and Memory] (http://www.reddit.com/r/AskHistorians/comments/38l4gf/why_were_the_soldiers_after_ww1_seemingly_so_much/)
• [WWI v WWII: The 'Bad War' vs The 'Good War'?] (http://www.reddit.com/r/AskHistorians/comments/37vqut/were_nazi_germany_and_imperial_japans_war_crimes/)
• [Combat in WWI and WWII] (http://www.reddit.com/r/AskHistorians/comments/39c6sd/did_we_know_the_rate_of_survival_during_the_world/)
• [Given the nationalistic fervour at the beginning of WWI, how many men were 'expected' to die?] (https://www.reddit.com/r/AskHistorians/comments/3eaz7v/given_the_nationalistic_fervor_for_war_at_its/)
• [To what extent was WWI inevitable?] (https://www.reddit.com/r/AskHistorians/comments/3faq1j/i_have_always_heard_war_was_inevitable_prior_to/)

Furthermore:

then the horrid sufferfest it turned out to be

And WWII didn't turn out to be a 'horrid sufferfest'? Just because we (ie the Anglosphere) didn't have a Wilfred Owen penning sonnets about it, doesn't mean WWII was a terrible, horrible conflict. WWI doesn't hold a candle to it.