As someone who was recruited to a financial firm a year ago to execute a modernization effort, I think the difference is due to (simplified) two types of firms: Big ones with huge moats often protected by regulators and profitability, and ones that are insecure. There is a pretty big population of companies that are at huge risk of being disrupted in the best sense of that term, and that's why they need to modernize. Many of these outdated core systems don't have modern capabilities, such as being desktop apps that can't integrate with the web or provide/use APIs without heavy refactoring anyway.