If failure is rare and recovery is easy then why would you want a more complicated protocol?

It frequently ran in environment where packet loss was rare and if there was a problem it was easy enough to run it again. + tftp was generally regarded as 'good enough'. + the files being transmitted were generally pretty small which reduces the opportunity for errors and makes recovery from error pretty easy.

+ tftp requires less memory than ftp which in the early days was attractive. + tftp is a more simple protocol as compared to ftp etc and especially in the early days the lower overhead was attractive. The original post asks this question ' why people prefer to use this unreliable TFTP to download files?' I believe that there are several possible answers Interestingly the Cisco implementation of tftp for copying to/from a Cisco device does have a mechanism to check for packet delivery and if a packet were to be dropped the Cisco tftp would detect this and generate an error.

yes the tftp protocol itself as a UDP protocol does not have a reliability mechanism.

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