A crummy user experience is rarely caused by a single overarching problem. Major issues are usually discovered and remedied in the design and development phases (but not always).
Most of the time, a crummy user experience is the result of many smaller but still grating issues that cause friction, fatigue, frustration and, eventually, failure. These are the thousand cuts of a bad user experience: broken buttons, confusing labels, outdated content, unhelpful error messages, and so on.
"The details are not the details. They make the design."—Charles Eames
Most organizations, however, are perpetually in Projects and Initiatives mode, not fix-it mode. They're chasing the enticing shiny ball, and ignoring all the broken toys strewn around the play room. They're so focused on What's Next that they're building mountains of tech and product debt.
The recent, enthusiastic embrace of the MVP as a preferred means of releasing products and services isn't helping things: before they've made their minimally viable products more viable, organizations are on to the next initiative, leaving frustrated users in their wake.
My advice? Eat your own dog food; I'm constantly amazed how few people use the stuff they offer others. Do frequent user observation and testing. Listen to your customer support team. Scrutinize your analytics for abandonment points. Keep an eye on social media. Dedicate time and resources to regular housekeeping.
Most of all: have pride in what you do. If you're comfortable with lots of little failures, you probably deserve the inevitable big failure that's surely headed your way.