Burke and Wills expedition was not considered to be a failure as such. Yes, they both died, but they completed their mission which was to successfully cross the continent from south to north (first Europeans to do this). Additionally their team collected valuable scientific information (botanical, meterological etc) and opened up great swathes of Queensland to explore for pastoral land. The numerous search parties set out also helped map and explore land unknown to europeans.

The question of why Burke and Wills were, and are to this day, celebrated is due to the cultural, political and social climate of Melbourne at the time. Burke and Wills set out in 1860. Melbourne had only been founded as a colony since 1836 (24yrs) and had only prospered since gold was struck in 1850. Although there was a massive influx of people after 1850 the colony was small and many people were in the goldfields not in Melbourne town. Melbourne was still small with not much going on. Melbourne and surrounding towns were becoming increasingly more prosperous. People were looking to explore new lands and new trade routes and be "the first". The journey was hyped up and great fanfare was made of it. It was backed by the Victorian government and the Victorian exploration society. It was a big exciting thing, happening in a small place where the race to dominate and explore was still ever present. Also the place was small enough that a lot of people would have met or known Burke and Wills personally.

https://www.hothamhistory.org.au/1006-2/ https://www.australiangeographic.com.au/topics/science-environment/2011/07/burke-and-wills-botanys-untold-success-story/ https://blogs.archives.qld.gov.au/2016/08/11/the-burke-and-wills-expedition-tragedy-and-triumph/ https://australianmuseum.net.au/about/history/exhibitions/trailblazers/burke-and-wills/ https://trove.nla.gov.au/newspaper/article/7271119