Literally because one guy said so and others latched onto it. It's like he never wrote in ML/ASM at the time. Nothing wrong with goto, its not bad. There are bad usages of course. I look at the "goto bad" folks as dumb asses following an unvetted religious assertion, and I'd love to see them program in ML. Their code would be bloated shitware.

What is more important is to document, especially strings, and complex functions. I found an old phreak tool/code hacker I wrote in 1988 on a the scene database. The gotos are not what makes it hard to follow. It's my various string handlers and no documentation of my variables.

Structured programming is a great idea; but not necessary for readable or useful code. Further, this religious bullshit killed many of the 'i program for myself' coders by making simple things more complex. Good programming means understanding the tools you have and implementing them to serve your desired ends. Goto allows for smaller code in certain situations, along with easier to read code in others. As line numbers were replaced with labels (like in qb4.5) readability options also increased.

10 print "i love goto! ";
20 goto 10

or

home
print "i still love goto! ";
goto home

TLDR: some jackass who didn't consider ML said something stupid about spaghetti code and readability and people took it as religious fact.