Hi, always more that can be said but these older answers may be of some interest to you:

https://www.reddit.com/r/AskHistorians/comments/ehni9g/why_are_worlds_fairs_no_longer_very_renowned/

and

https://www.reddit.com/r/AskHistorians/comments/3nc9nb/why_did_world_fairs_stop_being_a_big_things/