Actually, it's pretty simple.

"Better" has to actually "be better ENOUGH" to warrant all of the retooling of existing systems. I've got plenty of clients who would happily run Windows 2003 ("it's paid for") if it weren't for changing standards that aren't compatible (newer TLS, Exchange, etc) and security breaches. They only upgrade because they have to. "E-mail is e-mail" to them.

But if you sell them some magical new technology that promises to meet new features, like tons of data analysis tools and easily graphs and charts in a new version of CRM, they'll happily upgrade.