Don't know why people choose older stack for development of new project.

It's always good to wait for software to become more mature. Especially for large enterprise project from which you know their lifespan will at least be a couple of years.

For more short term projects, like branding websites for example, you can try out new stuff.

Also, end-to-end testing helps with new software that tends to get major refactoring in it's younger years.

@DevotedSniper What I mean by old is an extremely old stack. like something on PHP4.7 or python2 or java 6

@DevotedSniper But some people still use plain ASP.