The software is "easy", it's the business and operations that are hard: scaling the infrastructure reliably; finding revenue sources with secure margins; deflecting regulatory and risks responsibility; billing and collecting on massive low-margin high-volume transactions; enterprise sales; etc

It's a business line more suited to finance, law, sales, and accounting people than tech people and a pretty laborious one. That's often the case when the tech looks "easy" but the sector only seems to have a few big winners.