Why software such as Salesforce and Jira are successful marketwise?

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.

One, if there are great, intuitive, affordable alternatives, they are not widely known.

Two, the downsides of Salesforce and Jira are at least well known and widely discussed. If you have an issue, probably somebody else has had the same issue, and a workaround may be known.

Three, "nobody got fired for choosing..." used to end with "IBM", now it ends with "SAP", "Salesforce", "git", "Quickbooks", or "Jira". None of them are so great, but they all work well enough to get the job done (since many reasonably successful companies use them).

I agree they aren't that great, though.

Stockholm syndrome. At a startup, both were chosen. Why? Because that's what everyone used at their past employers. Also, is it worth the time investigating and debating which alternatives to use? If you are small, you probably have way more important things to attend to. If you are big, it's probably too late to change.