Marketing. There are plenty of alternatives for ERP and project management but non of them are so aggressively marketed. In germany most big business run SAP. Why? Is SAP technically better than anything else? No, but their sales people play golf with the relevant CEOs and CTOs. Developers are rarely or never asked which business tools to buy although we’re the only ones who could possibly evaluate them with some competence. "No one gets fired for buying IBM" - today you could replace it with SAP, Salesforce or even Jira. Btw, the same is true for web frameworks and even some programming languages.